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 $54.66   13.208%   $61.8795   $61.88   $61.90   $61.90  
  Purchase #2 $232.90   11.815%   $260.4171   $260.42   $260.40   $260.40  
  Purchase #3 $164.39   5.446%   $173.3427   $173.34   $173.35   $173.30  
  Purchase #4 $182.32   8.287%   $197.4289   $197.43   $197.45   $197.40  
  Purchase #5 $70.63   5.363%   $74.4179   $74.42   $74.40   $74.40  
  Purchase #6 $199.85   12.846%   $225.5227   $225.52   $225.50   $225.50  
  Purchase #7 $229.71   10.626%   $254.119   $254.12   $254.10   $254.10  
  7 purchase totals = $1,134.46       $1,247.1278   $1,247.13   $1,247.10   $1,247.00