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 $38.53   13.284%   $43.6483   $43.65   $43.65   $43.60  
  Purchase #2 $104.58   13.755%   $118.965   $118.97   $118.95   $119.00  
  Purchase #3 $46.89   4.519%   $49.009   $49.01   $49.00   $49.00  
  Purchase #4 $158.98   6.780%   $169.7588   $169.76   $169.75   $169.80  
  Purchase #5 $50.95   5.221%   $53.6101   $53.61   $53.60   $53.60  
  Purchase #6 $53.32   13.166%   $60.3401   $60.34   $60.35   $60.30  
  Purchase #7 $92.80   10.423%   $102.4725   $102.47   $102.45   $102.50  
  7 purchase totals = $546.05       $597.8038   $597.81   $597.75   $597.80