Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $201.94   7.827%   $217.7458   $217.75   $217.75   $217.70  
  Purchase #2 $25.42   6.104%   $26.9716   $26.97   $26.95   $27.00  
  Purchase #3 $65.58   10.447%   $72.4311   $72.43   $72.45   $72.40  
  Purchase #4 $211.97   9.773%   $232.6858   $232.69   $232.70   $232.70  
  Purchase #5 $199.73   12.234%   $224.165   $224.17   $224.15   $224.20  
  Purchase #6 $139.50   12.679%   $157.1872   $157.19   $157.20   $157.20  
  Purchase #7 $240.65   13.869%   $274.0257   $274.03   $274.05   $274.00  
  7 purchase totals = $1,084.79       $1,205.2122   $1,205.23   $1,205.25   $1,205.20