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 $84.48   9.733%   $92.7024   $92.70   $92.70   $92.70  
  Purchase #2 $157.38   11.109%   $174.8633   $174.86   $174.85   $174.90  
  Purchase #3 $68.90   6.109%   $73.1091   $73.11   $73.10   $73.10  
  Purchase #4 $121.56   7.282%   $130.412   $130.41   $130.40   $130.40  
  Purchase #5 $198.75   8.862%   $216.3632   $216.36   $216.35   $216.40  
  Purchase #6 $170.93   8.245%   $185.0232   $185.02   $185.00   $185.00  
  Purchase #7 $68.41   8.413%   $74.1653   $74.17   $74.15   $74.20  
  7 purchase totals = $870.41       $946.6385   $946.63   $946.55   $946.70