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 $84.99   10.592%   $93.9921   $93.99   $94.00   $94.00  
  Purchase #2 $62.55   6.186%   $66.4193   $66.42   $66.40   $66.40  
  Purchase #3 $94.89   8.591%   $103.042   $103.04   $103.05   $103.00  
  Purchase #4 $233.60   3.221%   $241.1243   $241.12   $241.10   $241.10  
  Purchase #5 $89.53   9.559%   $98.0882   $98.09   $98.10   $98.10  
  Purchase #6 $156.26   5.496%   $164.848   $164.85   $164.85   $164.80  
  Purchase #7 $166.89   13.813%   $189.9425   $189.94   $189.95   $189.90  
  7 purchase totals = $888.71       $957.4564   $957.45   $957.45   $957.30