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 $84.90   13.733%   $96.5593   $96.56   $96.55   $96.60  
  Purchase #2 $181.76   8.557%   $197.3132   $197.31   $197.30   $197.30  
  Purchase #3 $152.56   3.754%   $158.2871   $158.29   $158.30   $158.30  
  Purchase #4 $66.88   4.381%   $69.81   $69.81   $69.80   $69.80  
  Purchase #5 $138.99   13.148%   $157.2644   $157.26   $157.25   $157.30  
  Purchase #6 $171.36   9.139%   $187.0206   $187.02   $187.00   $187.00  
  Purchase #7 $62.79   6.611%   $66.941   $66.94   $66.95   $66.90  
  7 purchase totals = $859.24       $933.1956   $933.19   $933.15   $933.20