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 $88.69   7.593%   $95.4242   $95.42   $95.40   $95.40  
  Purchase #2 $7.79   5.262%   $8.1999   $8.20   $8.20   $8.20  
  Purchase #3 $229.67   4.557%   $240.1361   $240.14   $240.15   $240.10  
  Purchase #4 $64.28   3.474%   $66.5131   $66.51   $66.50   $66.50  
  Purchase #5 $116.53   12.583%   $131.193   $131.19   $131.20   $131.20  
  Purchase #6 $124.65   5.591%   $131.6192   $131.62   $131.60   $131.60  
  Purchase #7 $249.54   5.383%   $262.9727   $262.97   $262.95   $263.00  
  7 purchase totals = $881.15       $936.0582   $936.05   $936.00   $936.00