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 $18.78   8.481%   $20.3727   $20.37   $20.35   $20.40  
  Purchase #2 $205.53   7.128%   $220.1802   $220.18   $220.20   $220.20  
  Purchase #3 $91.29   4.435%   $95.3387   $95.34   $95.35   $95.30  
  Purchase #4 $244.28   11.117%   $271.4366   $271.44   $271.45   $271.40  
  Purchase #5 $29.25   6.603%   $31.1814   $31.18   $31.20   $31.20  
  Purchase #6 $76.43   13.541%   $86.7794   $86.78   $86.80   $86.80  
  Purchase #7 $40.43   8.583%   $43.9001   $43.90   $43.90   $43.90  
  7 purchase totals = $705.99       $769.1891   $769.19   $769.25   $769.20