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 $214.94   12.135%   $241.023   $241.02   $241.00   $241.00  
  Purchase #2 $72.27   10.775%   $80.0571   $80.06   $80.05   $80.10  
  Purchase #3 $55.39   12.715%   $62.4328   $62.43   $62.45   $62.40  
  Purchase #4 $44.71   8.420%   $48.4746   $48.47   $48.45   $48.50  
  Purchase #5 $49.86   3.589%   $51.6495   $51.65   $51.65   $51.60  
  Purchase #6 $92.44   12.713%   $104.1919   $104.19   $104.20   $104.20  
  Purchase #7 $84.45   10.461%   $93.2843   $93.28   $93.30   $93.30  
  7 purchase totals = $614.06       $681.1132   $681.10   $681.10   $681.10