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 $60.27   3.413%   $62.327   $62.33   $62.35   $62.30  
  Purchase #2 $65.54   3.695%   $67.9617   $67.96   $67.95   $68.00  
  Purchase #3 $29.60   5.203%   $31.1401   $31.14   $31.15   $31.10  
  Purchase #4 $237.83   3.732%   $246.7058   $246.71   $246.70   $246.70  
  Purchase #5 $132.69   3.164%   $136.8883   $136.89   $136.90   $136.90  
  Purchase #6 $40.43   9.157%   $44.1322   $44.13   $44.15   $44.10  
  Purchase #7 $59.63   12.315%   $66.9734   $66.97   $66.95   $67.00  
  7 purchase totals = $625.99       $656.1285   $656.13   $656.15   $656.10