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 $121.38   3.503%   $125.6319   $125.63   $125.65   $125.60  
  Purchase #2 $208.57   6.275%   $221.6578   $221.66   $221.65   $221.70  
  Purchase #3 $117.96   6.577%   $125.7182   $125.72   $125.70   $125.70  
  Purchase #4 $110.58   12.705%   $124.6292   $124.63   $124.65   $124.60  
  Purchase #5 $90.71   6.566%   $96.666   $96.67   $96.65   $96.70  
  Purchase #6 $187.72   11.848%   $209.9611   $209.96   $209.95   $210.00  
  Purchase #7 $92.54   8.132%   $100.0654   $100.07   $100.05   $100.10  
  7 purchase totals = $929.46       $1,004.3296   $1,004.34   $1,004.30   $1,004.40