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 $66.33   13.305%   $75.1552   $75.16   $75.15   $75.20  
  Purchase #2 $40.39   8.330%   $43.7545   $43.75   $43.75   $43.80  
  Purchase #3 $194.49   3.469%   $201.2369   $201.24   $201.25   $201.20  
  Purchase #4 $84.77   3.772%   $87.9675   $87.97   $87.95   $88.00  
  Purchase #5 $12.66   6.523%   $13.4858   $13.49   $13.50   $13.50  
  Purchase #6 $232.41   12.598%   $261.689   $261.69   $261.70   $261.70  
  Purchase #7 $36.54   12.634%   $41.1565   $41.16   $41.15   $41.20  
  7 purchase totals = $667.59       $724.4454   $724.46   $724.45   $724.60