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 $70.33   4.552%   $73.5314   $73.53   $73.55   $73.50  
  Purchase #2 $211.96   11.583%   $236.5113   $236.51   $236.50   $236.50  
  Purchase #3 $216.96   3.429%   $224.3996   $224.40   $224.40   $224.40  
  Purchase #4 $122.35   12.318%   $137.4211   $137.42   $137.40   $137.40  
  Purchase #5 $186.58   8.683%   $202.7807   $202.78   $202.80   $202.80  
  Purchase #6 $227.63   12.387%   $255.8265   $255.83   $255.85   $255.80  
  Purchase #7 $224.45   4.347%   $234.2068   $234.21   $234.20   $234.20  
  7 purchase totals = $1,260.26       $1,364.6774   $1,364.68   $1,364.70   $1,364.60