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 $97.35   6.561%   $103.7371   $103.74   $103.75   $103.70  
  Purchase #2 $79.97   10.369%   $88.2621   $88.26   $88.25   $88.30  
  Purchase #3 $138.52   4.400%   $144.6149   $144.61   $144.60   $144.60  
  Purchase #4 $233.86   3.654%   $242.4052   $242.41   $242.40   $242.40  
  Purchase #5 $194.42   4.307%   $202.7937   $202.79   $202.80   $202.80  
  Purchase #6 $85.27   8.624%   $92.6237   $92.62   $92.60   $92.60  
  Purchase #7 $87.50   7.189%   $93.7904   $93.79   $93.80   $93.80  
  7 purchase totals = $916.89       $968.2271   $968.22   $968.20   $968.20