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 $87.47   12.176%   $98.1203   $98.12   $98.10   $98.10  
  Purchase #2 $63.38   4.575%   $66.2796   $66.28   $66.30   $66.30  
  Purchase #3 $175.73   4.494%   $183.6273   $183.63   $183.65   $183.60  
  Purchase #4 $218.39   10.633%   $241.6114   $241.61   $241.60   $241.60  
  Purchase #5 $134.98   8.868%   $146.95   $146.95   $146.95   $147.00  
  Purchase #6 $114.62   9.280%   $125.2567   $125.26   $125.25   $125.30  
  Purchase #7 $126.28   10.327%   $139.3209   $139.32   $139.30   $139.30  
  7 purchase totals = $920.85       $1,001.1662   $1,001.17   $1,001.15   $1,001.20