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 $9.88   12.843%   $11.1489   $11.15   $11.15   $11.10  
  Purchase #2 $212.71   10.743%   $235.5614   $235.56   $235.55   $235.60  
  Purchase #3 $15.48   11.697%   $17.2907   $17.29   $17.30   $17.30  
  Purchase #4 $215.63   9.541%   $236.2033   $236.20   $236.20   $236.20  
  Purchase #5 $209.71   13.439%   $237.8929   $237.89   $237.90   $237.90  
  Purchase #6 $217.45   10.487%   $240.254   $240.25   $240.25   $240.30  
  Purchase #7 $14.40   12.746%   $16.2354   $16.24   $16.25   $16.20  
  7 purchase totals = $895.26       $994.5866   $994.58   $994.60   $994.60