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 $91.96   4.792%   $96.3667   $96.37   $96.35   $96.40  
  Purchase #2 $169.58   6.468%   $180.5484   $180.55   $180.55   $180.50  
  Purchase #3 $59.47   5.635%   $62.8211   $62.82   $62.80   $62.80  
  Purchase #4 $76.56   8.716%   $83.233   $83.23   $83.25   $83.20  
  Purchase #5 $130.49   9.185%   $142.4755   $142.48   $142.50   $142.50  
  Purchase #6 $177.83   13.588%   $201.9935   $201.99   $202.00   $202.00  
  Purchase #7 $139.87   3.451%   $144.6969   $144.70   $144.70   $144.70  
  7 purchase totals = $845.76       $912.1351   $912.14   $912.15   $912.10