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 $197.51   3.813%   $205.0411   $205.04   $205.05   $205.00  
  Purchase #2 $25.34   4.232%   $26.4124   $26.41   $26.40   $26.40  
  Purchase #3 $189.34   12.581%   $213.1609   $213.16   $213.15   $213.20  
  Purchase #4 $161.53   5.178%   $169.894   $169.89   $169.90   $169.90  
  Purchase #5 $244.71   3.389%   $253.0032   $253.00   $253.00   $253.00  
  Purchase #6 $110.45   13.237%   $125.0703   $125.07   $125.05   $125.10  
  Purchase #7 $229.69   5.467%   $242.2472   $242.25   $242.25   $242.20  
  7 purchase totals = $1,158.57       $1,234.8291   $1,234.82   $1,234.80   $1,234.80