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 $60.48   11.220%   $67.2659   $67.27   $67.25   $67.30  
  Purchase #2 $85.32   9.334%   $93.2838   $93.28   $93.30   $93.30  
  Purchase #3 $245.56   11.767%   $274.455   $274.46   $274.45   $274.50  
  Purchase #4 $231.43   13.448%   $262.5527   $262.55   $262.55   $262.60  
  Purchase #5 $126.81   11.422%   $141.2942   $141.29   $141.30   $141.30  
  Purchase #6 $32.37   10.808%   $35.8685   $35.87   $35.85   $35.90  
  Purchase #7 $203.73   7.246%   $218.4923   $218.49   $218.50   $218.50  
  7 purchase totals = $985.70       $1,093.2124   $1,093.21   $1,093.20   $1,093.40