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 $54.56   13.780%   $62.0784   $62.08   $62.10   $62.10  
  Purchase #2 $141.47   11.824%   $158.1974   $158.20   $158.20   $158.20  
  Purchase #3 $68.40   12.156%   $76.7147   $76.71   $76.70   $76.70  
  Purchase #4 $27.71   10.415%   $30.596   $30.60   $30.60   $30.60  
  Purchase #5 $132.89   8.725%   $144.4847   $144.48   $144.50   $144.50  
  Purchase #6 $87.46   8.527%   $94.9177   $94.92   $94.90   $94.90  
  Purchase #7 $122.51   10.228%   $135.0403   $135.04   $135.05   $135.00  
  7 purchase totals = $635.00       $702.0292   $702.03   $702.05   $702.00