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 $247.90   13.733%   $281.9441   $281.94   $281.95   $281.90  
  Purchase #2 $62.44   11.111%   $69.3777   $69.38   $69.40   $69.40  
  Purchase #3 $127.96   4.752%   $134.0407   $134.04   $134.05   $134.00  
  Purchase #4 $173.65   13.473%   $197.0459   $197.05   $197.05   $197.00  
  Purchase #5 $125.82   5.874%   $133.2107   $133.21   $133.20   $133.20  
  Purchase #6 $5.29   11.603%   $5.9038   $5.90   $5.90   $5.90  
  Purchase #7 $120.94   9.278%   $132.1608   $132.16   $132.15   $132.20  
  7 purchase totals = $864.00       $953.6837   $953.68   $953.70   $953.60