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 $178.97   8.725%   $194.5851   $194.59   $194.60   $194.60  
  Purchase #2 $101.38   9.540%   $111.0517   $111.05   $111.05   $111.10  
  Purchase #3 $222.77   12.332%   $250.242   $250.24   $250.25   $250.20  
  Purchase #4 $125.62   7.861%   $135.495   $135.50   $135.50   $135.50  
  Purchase #5 $18.27   3.615%   $18.9305   $18.93   $18.95   $18.90  
  Purchase #6 $124.28   4.367%   $129.7073   $129.71   $129.70   $129.70  
  Purchase #7 $217.72   7.546%   $234.1492   $234.15   $234.15   $234.10  
  7 purchase totals = $989.01       $1,074.1608   $1,074.17   $1,074.20   $1,074.10