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 $219.65   12.113%   $246.2562   $246.26   $246.25   $246.30  
  Purchase #2 $230.28   5.382%   $242.6737   $242.67   $242.65   $242.70  
  Purchase #3 $225.40   13.422%   $255.6532   $255.65   $255.65   $255.70  
  Purchase #4 $91.82   8.242%   $99.3878   $99.39   $99.40   $99.40  
  Purchase #5 $73.95   8.299%   $80.0871   $80.09   $80.10   $80.10  
  Purchase #6 $237.53   8.741%   $258.2925   $258.29   $258.30   $258.30  
  Purchase #7 $235.68   12.733%   $265.6891   $265.69   $265.70   $265.70  
  7 purchase totals = $1,314.31       $1,448.0396   $1,448.04   $1,448.05   $1,448.20