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 $59.82   12.778%   $67.4638   $67.46   $67.45   $67.50  
  Purchase #2 $136.38   12.804%   $153.8421   $153.84   $153.85   $153.80  
  Purchase #3 $154.73   3.812%   $160.6283   $160.63   $160.65   $160.60  
  Purchase #4 $67.62   11.816%   $75.61   $75.61   $75.60   $75.60  
  Purchase #5 $236.42   5.557%   $249.5579   $249.56   $249.55   $249.60  
  Purchase #6 $190.70   12.691%   $214.9017   $214.90   $214.90   $214.90  
  Purchase #7 $223.46   6.611%   $238.2329   $238.23   $238.25   $238.20  
  7 purchase totals = $1,069.13       $1,160.2367   $1,160.23   $1,160.25   $1,160.20