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 $40.92   5.724%   $43.2623   $43.26   $43.25   $43.30  
  Purchase #2 $112.82   5.301%   $118.8006   $118.80   $118.80   $118.80  
  Purchase #3 $123.73   6.408%   $131.6586   $131.66   $131.65   $131.70  
  Purchase #4 $181.36   7.496%   $194.9547   $194.95   $194.95   $195.00  
  Purchase #5 $89.39   3.149%   $92.2049   $92.20   $92.20   $92.20  
  Purchase #6 $142.70   12.588%   $160.6631   $160.66   $160.65   $160.70  
  Purchase #7 $49.86   5.804%   $52.7539   $52.75   $52.75   $52.80  
  7 purchase totals = $740.78       $794.2981   $794.28   $794.25   $794.50