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 $246.39   12.704%   $277.6914   $277.69   $277.70   $277.70  
  Purchase #2 $138.81   10.762%   $153.7487   $153.75   $153.75   $153.70  
  Purchase #3 $87.56   12.115%   $98.1679   $98.17   $98.15   $98.20  
  Purchase #4 $119.90   11.277%   $133.4211   $133.42   $133.40   $133.40  
  Purchase #5 $60.41   4.810%   $63.3157   $63.32   $63.30   $63.30  
  Purchase #6 $238.29   4.865%   $249.8828   $249.88   $249.90   $249.90  
  Purchase #7 $157.31   10.293%   $173.5019   $173.50   $173.50   $173.50  
  7 purchase totals = $1,048.67       $1,149.7295   $1,149.73   $1,149.70   $1,149.70