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 $115.44   3.108%   $119.0279   $119.03   $119.05   $119.00  
  Purchase #2 $148.41   10.873%   $164.5466   $164.55   $164.55   $164.50  
  Purchase #3 $196.32   8.262%   $212.54   $212.54   $212.55   $212.50  
  Purchase #4 $231.84   13.680%   $263.5557   $263.56   $263.55   $263.60  
  Purchase #5 $5.83   11.612%   $6.507   $6.51   $6.50   $6.50  
  Purchase #6 $116.79   7.326%   $125.346   $125.35   $125.35   $125.30  
  Purchase #7 $229.80   13.231%   $260.2048   $260.20   $260.20   $260.20  
  7 purchase totals = $1,044.43       $1,151.7280   $1,151.74   $1,151.75   $1,151.60