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 $177.28   11.329%   $197.3641   $197.36   $197.35   $197.40  
  Purchase #2 $42.71   8.751%   $46.4476   $46.45   $46.45   $46.40  
  Purchase #3 $138.87   8.179%   $150.2282   $150.23   $150.25   $150.20  
  Purchase #4 $125.78   7.627%   $135.3732   $135.37   $135.35   $135.40  
  Purchase #5 $18.55   7.266%   $19.8978   $19.90   $19.90   $19.90  
  Purchase #6 $243.61   5.756%   $257.6322   $257.63   $257.65   $257.60  
  Purchase #7 $205.54   5.578%   $217.005   $217.01   $217.00   $217.00  
  7 purchase totals = $952.34       $1,023.9481   $1,023.95   $1,023.95   $1,023.90