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 $248.74   10.757%   $275.497   $275.50   $275.50   $275.50  
  Purchase #2 $205.42   7.679%   $221.1942   $221.19   $221.20   $221.20  
  Purchase #3 $61.67   7.450%   $66.2644   $66.26   $66.25   $66.30  
  Purchase #4 $104.63   4.288%   $109.1165   $109.12   $109.10   $109.10  
  Purchase #5 $146.82   9.337%   $160.5286   $160.53   $160.55   $160.50  
  Purchase #6 $77.59   12.489%   $87.2802   $87.28   $87.30   $87.30  
  Purchase #7 $242.93   3.204%   $250.7135   $250.71   $250.70   $250.70  
  7 purchase totals = $1,087.80       $1,170.5944   $1,170.59   $1,170.60   $1,170.60