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 $54.96   3.586%   $56.9309   $56.93   $56.95   $56.90  
  Purchase #2 $90.81   4.392%   $94.7984   $94.80   $94.80   $94.80  
  Purchase #3 $59.39   5.260%   $62.5139   $62.51   $62.50   $62.50  
  Purchase #4 $178.41   5.225%   $187.7319   $187.73   $187.75   $187.70  
  Purchase #5 $86.78   3.861%   $90.1306   $90.13   $90.15   $90.10  
  Purchase #6 $88.72   3.611%   $91.9237   $91.92   $91.90   $91.90  
  Purchase #7 $119.87   13.193%   $135.6844   $135.68   $135.70   $135.70  
  7 purchase totals = $678.94       $719.7138   $719.70   $719.75   $719.60