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 $190.69   5.468%   $201.1169   $201.12   $201.10   $201.10  
  Purchase #2 $19.39   6.245%   $20.6009   $20.60   $20.60   $20.60  
  Purchase #3 $160.28   4.352%   $167.2554   $167.26   $167.25   $167.30  
  Purchase #4 $103.91   6.507%   $110.6714   $110.67   $110.65   $110.70  
  Purchase #5 $236.86   13.124%   $267.9455   $267.95   $267.95   $267.90  
  Purchase #6 $89.70   8.143%   $97.0043   $97.00   $97.00   $97.00  
  Purchase #7 $160.92   12.141%   $180.4573   $180.46   $180.45   $180.50  
  7 purchase totals = $961.75       $1,045.0517   $1,045.06   $1,045.00   $1,045.10