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 $250.85   10.120%   $276.236   $276.24   $276.25   $276.20  
  Purchase #2 $110.32   8.574%   $119.7788   $119.78   $119.80   $119.80  
  Purchase #3 $10.60   12.792%   $11.956   $11.96   $11.95   $12.00  
  Purchase #4 $72.64   7.181%   $77.8563   $77.86   $77.85   $77.90  
  Purchase #5 $168.29   10.129%   $185.3361   $185.34   $185.35   $185.30  
  Purchase #6 $244.39   6.566%   $260.4366   $260.44   $260.45   $260.40  
  Purchase #7 $246.32   5.499%   $259.8651   $259.87   $259.85   $259.90  
  7 purchase totals = $1,103.41       $1,191.4649   $1,191.49   $1,191.50   $1,191.50