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 $190.68   11.860%   $213.2946   $213.29   $213.30   $213.30  
  Purchase #2 $81.61   5.779%   $86.3262   $86.33   $86.35   $86.30  
  Purchase #3 $100.83   3.441%   $104.2996   $104.30   $104.30   $104.30  
  Purchase #4 $73.55   3.644%   $76.2302   $76.23   $76.25   $76.20  
  Purchase #5 $62.49   7.175%   $66.9737   $66.97   $66.95   $67.00  
  Purchase #6 $243.53   13.474%   $276.3432   $276.34   $276.35   $276.30  
  Purchase #7 $175.26   13.753%   $199.3635   $199.36   $199.35   $199.40  
  7 purchase totals = $927.95       $1,022.8310   $1,022.82   $1,022.85   $1,022.80