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   5.735%   $259.9706   $259.97   $259.95   $260.00  
  Purchase #2 $171.25   9.622%   $187.7277   $187.73   $187.75   $187.70  
  Purchase #3 $124.51   6.488%   $132.5882   $132.59   $132.60   $132.60  
  Purchase #4 $121.35   6.130%   $128.7888   $128.79   $128.80   $128.80  
  Purchase #5 $188.61   11.635%   $210.5548   $210.55   $210.55   $210.60  
  Purchase #6 $248.70   11.182%   $276.5096   $276.51   $276.50   $276.50  
  Purchase #7 $27.91   9.327%   $30.5132   $30.51   $30.50   $30.50  
  7 purchase totals = $1,128.20       $1,226.6529   $1,226.65   $1,226.65   $1,226.70