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 $127.38   5.684%   $134.6203   $134.62   $134.60   $134.60  
  Purchase #2 $98.38   13.560%   $111.7203   $111.72   $111.70   $111.70  
  Purchase #3 $193.97   9.183%   $211.7823   $211.78   $211.80   $211.80  
  Purchase #4 $88.76   9.571%   $97.2552   $97.26   $97.25   $97.30  
  Purchase #5 $130.67   4.697%   $136.8076   $136.81   $136.80   $136.80  
  Purchase #6 $56.51   9.505%   $61.8813   $61.88   $61.90   $61.90  
  Purchase #7 $202.79   7.177%   $217.3442   $217.34   $217.35   $217.30  
  7 purchase totals = $898.46       $971.4112   $971.41   $971.40   $971.40