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 $216.82   12.362%   $243.6233   $243.62   $243.60   $243.60  
  Purchase #2 $29.56   9.549%   $32.3827   $32.38   $32.40   $32.40  
  Purchase #3 $236.86   5.809%   $250.6192   $250.62   $250.60   $250.60  
  Purchase #4 $244.67   12.838%   $276.0807   $276.08   $276.10   $276.10  
  Purchase #5 $51.34   12.145%   $57.5752   $57.58   $57.60   $57.60  
  Purchase #6 $184.73   3.391%   $190.9942   $190.99   $191.00   $191.00  
  Purchase #7 $148.87   6.332%   $158.2964   $158.30   $158.30   $158.30  
  7 purchase totals = $1,112.85       $1,209.5717   $1,209.57   $1,209.60   $1,209.60