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 $90.69   13.120%   $102.5885   $102.59   $102.60   $102.60  
  Purchase #2 $203.31   3.773%   $210.9809   $210.98   $211.00   $211.00  
  Purchase #3 $89.53   3.424%   $92.5955   $92.60   $92.60   $92.60  
  Purchase #4 $157.46   10.496%   $173.987   $173.99   $174.00   $174.00  
  Purchase #5 $238.68   11.571%   $266.2977   $266.30   $266.30   $266.30  
  Purchase #6 $147.74   8.666%   $160.5431   $160.54   $160.55   $160.50  
  Purchase #7 $19.50   3.713%   $20.224   $20.22   $20.20   $20.20  
  7 purchase totals = $946.91       $1,027.2167   $1,027.22   $1,027.25   $1,027.20