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 $163.60   13.551%   $185.7694   $185.77   $185.75   $185.80  
  Purchase #2 $15.25   11.797%   $17.049   $17.05   $17.05   $17.00  
  Purchase #3 $85.96   11.830%   $96.1291   $96.13   $96.15   $96.10  
  Purchase #4 $54.42   5.460%   $57.3913   $57.39   $57.40   $57.40  
  Purchase #5 $244.71   4.344%   $255.3402   $255.34   $255.35   $255.30  
  Purchase #6 $68.33   7.755%   $73.629   $73.63   $73.65   $73.60  
  Purchase #7 $97.61   11.711%   $109.0411   $109.04   $109.05   $109.00  
  7 purchase totals = $729.88       $794.3491   $794.35   $794.40   $794.20