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 $68.32   8.593%   $74.1907   $74.19   $74.20   $74.20  
  Purchase #2 $234.51   6.442%   $249.6171   $249.62   $249.60   $249.60  
  Purchase #3 $126.86   5.724%   $134.1215   $134.12   $134.10   $134.10  
  Purchase #4 $232.53   6.637%   $247.963   $247.96   $247.95   $248.00  
  Purchase #5 $240.55   7.647%   $258.9449   $258.94   $258.95   $258.90  
  Purchase #6 $42.95   8.391%   $46.5539   $46.55   $46.55   $46.60  
  Purchase #7 $177.40   12.863%   $200.219   $200.22   $200.20   $200.20  
  7 purchase totals = $1,123.12       $1,211.6101   $1,211.60   $1,211.55   $1,211.60