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 $241.67   11.123%   $268.551   $268.55   $268.55   $268.60  
  Purchase #2 $44.68   8.262%   $48.3715   $48.37   $48.35   $48.40  
  Purchase #3 $29.91   13.808%   $34.04   $34.04   $34.05   $34.00  
  Purchase #4 $246.94   13.141%   $279.3904   $279.39   $279.40   $279.40  
  Purchase #5 $195.73   10.574%   $216.4265   $216.43   $216.45   $216.40  
  Purchase #6 $10.68   7.177%   $11.4465   $11.45   $11.45   $11.40  
  Purchase #7 $169.33   7.555%   $182.1229   $182.12   $182.10   $182.10  
  7 purchase totals = $938.94       $1,040.3488   $1,040.35   $1,040.35   $1,040.30