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 $196.67   12.628%   $221.5055   $221.51   $221.50   $221.50  
  Purchase #2 $86.26   7.297%   $92.5544   $92.55   $92.55   $92.60  
  Purchase #3 $44.48   11.800%   $49.7286   $49.73   $49.75   $49.70  
  Purchase #4 $230.29   13.287%   $260.8886   $260.89   $260.90   $260.90  
  Purchase #5 $149.59   8.440%   $162.2154   $162.22   $162.20   $162.20  
  Purchase #6 $32.45   7.763%   $34.9691   $34.97   $34.95   $35.00  
  Purchase #7 $192.45   11.767%   $215.0956   $215.10   $215.10   $215.10  
  7 purchase totals = $932.19       $1,036.9572   $1,036.97   $1,036.95   $1,037.00