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 $152.58   13.617%   $173.3568   $173.36   $173.35   $173.40  
  Purchase #2 $23.93   12.325%   $26.8794   $26.88   $26.90   $26.90  
  Purchase #3 $72.53   5.737%   $76.691   $76.69   $76.70   $76.70  
  Purchase #4 $238.84   11.615%   $266.5813   $266.58   $266.60   $266.60  
  Purchase #5 $215.72   12.306%   $242.2665   $242.27   $242.25   $242.30  
  Purchase #6 $5.65   3.486%   $5.847   $5.85   $5.85   $5.80  
  Purchase #7 $184.65   10.733%   $204.4685   $204.47   $204.45   $204.50  
  7 purchase totals = $893.90       $996.0905   $996.10   $996.10   $996.20