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 $94.47   4.188%   $98.4264   $98.43   $98.45   $98.40  
  Purchase #2 $128.40   13.687%   $145.9741   $145.97   $145.95   $146.00  
  Purchase #3 $66.62   4.141%   $69.3787   $69.38   $69.40   $69.40  
  Purchase #4 $85.47   6.143%   $90.7204   $90.72   $90.70   $90.70  
  Purchase #5 $249.71   5.204%   $262.7049   $262.70   $262.70   $262.70  
  Purchase #6 $75.47   12.512%   $84.9128   $84.91   $84.90   $84.90  
  Purchase #7 $245.49   5.344%   $258.609   $258.61   $258.60   $258.60  
  7 purchase totals = $945.63       $1,010.7263   $1,010.72   $1,010.70   $1,010.70