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 $245.87   6.372%   $261.5368   $261.54   $261.55   $261.50  
  Purchase #2 $85.87   11.342%   $95.6094   $95.61   $95.60   $95.60  
  Purchase #3 $190.55   12.764%   $214.8718   $214.87   $214.85   $214.90  
  Purchase #4 $232.25   10.411%   $256.4295   $256.43   $256.45   $256.40  
  Purchase #5 $118.49   11.457%   $132.0654   $132.07   $132.05   $132.10  
  Purchase #6 $109.55   7.176%   $117.4113   $117.41   $117.40   $117.40  
  Purchase #7 $184.94   11.700%   $206.578   $206.58   $206.60   $206.60  
  7 purchase totals = $1,167.52       $1,284.5022   $1,284.51   $1,284.50   $1,284.50