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 $193.76   6.703%   $206.7477   $206.75   $206.75   $206.70  
  Purchase #2 $68.81   9.153%   $75.1082   $75.11   $75.10   $75.10  
  Purchase #3 $64.53   5.669%   $68.1882   $68.19   $68.20   $68.20  
  Purchase #4 $59.42   11.619%   $66.324   $66.32   $66.30   $66.30  
  Purchase #5 $151.42   9.750%   $166.1835   $166.18   $166.20   $166.20  
  Purchase #6 $52.47   10.511%   $57.9851   $57.99   $58.00   $58.00  
  Purchase #7 $135.62   9.286%   $148.2137   $148.21   $148.20   $148.20  
  7 purchase totals = $726.03       $788.7504   $788.75   $788.75   $788.70