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 $82.88   12.163%   $92.9607   $92.96   $92.95   $93.00  
  Purchase #2 $105.80   11.505%   $117.9723   $117.97   $117.95   $118.00  
  Purchase #3 $202.58   12.755%   $228.4191   $228.42   $228.40   $228.40  
  Purchase #4 $124.35   8.379%   $134.7693   $134.77   $134.75   $134.80  
  Purchase #5 $5.49   7.863%   $5.9217   $5.92   $5.90   $5.90  
  Purchase #6 $224.58   5.634%   $237.2328   $237.23   $237.25   $237.20  
  Purchase #7 $145.29   10.275%   $160.2185   $160.22   $160.20   $160.20  
  7 purchase totals = $890.97       $977.4944   $977.49   $977.40   $977.50