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 $103.38   13.469%   $117.3043   $117.30   $117.30   $117.30  
  Purchase #2 $177.78   7.527%   $191.1615   $191.16   $191.15   $191.20  
  Purchase #3 $137.51   10.487%   $151.9307   $151.93   $151.95   $151.90  
  Purchase #4 $112.53   9.391%   $123.0977   $123.10   $123.10   $123.10  
  Purchase #5 $197.60   9.811%   $216.9865   $216.99   $217.00   $217.00  
  Purchase #6 $97.29   6.709%   $103.8172   $103.82   $103.80   $103.80  
  Purchase #7 $85.51   8.447%   $92.733   $92.73   $92.75   $92.70  
  7 purchase totals = $911.60       $997.0309   $997.03   $997.05   $997.00