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 $10.71   9.790%   $11.7585   $11.76   $11.75   $11.80  
  Purchase #2 $227.60   3.846%   $236.3535   $236.35   $236.35   $236.40  
  Purchase #3 $117.78   8.869%   $128.2259   $128.23   $128.25   $128.20  
  Purchase #4 $243.52   5.676%   $257.3422   $257.34   $257.35   $257.30  
  Purchase #5 $239.79   10.557%   $265.1046   $265.10   $265.10   $265.10  
  Purchase #6 $157.45   5.700%   $166.4247   $166.42   $166.40   $166.40  
  Purchase #7 $126.95   10.508%   $140.2899   $140.29   $140.30   $140.30  
  7 purchase totals = $1,123.80       $1,205.4993   $1,205.49   $1,205.50   $1,205.50