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 $182.46   8.186%   $197.3962   $197.40   $197.40   $197.40  
  Purchase #2 $250.91   5.580%   $264.9108   $264.91   $264.90   $264.90  
  Purchase #3 $244.83   6.786%   $261.4442   $261.44   $261.45   $261.40  
  Purchase #4 $196.73   10.451%   $217.2903   $217.29   $217.30   $217.30  
  Purchase #5 $109.42   5.187%   $115.0956   $115.10   $115.10   $115.10  
  Purchase #6 $52.35   12.576%   $58.9335   $58.93   $58.95   $58.90  
  Purchase #7 $67.45   12.683%   $76.0047   $76.00   $76.00   $76.00  
  7 purchase totals = $1,104.15       $1,191.0753   $1,191.07   $1,191.10   $1,191.00