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 $66.37   12.594%   $74.7286   $74.73   $74.75   $74.70  
  Purchase #2 $211.39   11.411%   $235.5117   $235.51   $235.50   $235.50  
  Purchase #3 $146.60   13.580%   $166.5083   $166.51   $166.50   $166.50  
  Purchase #4 $96.58   7.840%   $104.1519   $104.15   $104.15   $104.20  
  Purchase #5 $71.82   13.299%   $81.3713   $81.37   $81.35   $81.40  
  Purchase #6 $15.82   4.427%   $16.5204   $16.52   $16.50   $16.50  
  Purchase #7 $71.51   6.474%   $76.1396   $76.14   $76.15   $76.10  
  7 purchase totals = $680.09       $754.9318   $754.93   $754.90   $754.90