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 $68.54   3.117%   $70.6764   $70.68   $70.70   $70.70  
  Purchase #2 $164.68   9.822%   $180.8549   $180.85   $180.85   $180.90  
  Purchase #3 $108.40   5.359%   $114.2092   $114.21   $114.20   $114.20  
  Purchase #4 $106.95   11.787%   $119.5562   $119.56   $119.55   $119.60  
  Purchase #5 $175.58   12.414%   $197.3765   $197.38   $197.40   $197.40  
  Purchase #6 $81.62   6.720%   $87.1049   $87.10   $87.10   $87.10  
  Purchase #7 $119.63   4.566%   $125.0923   $125.09   $125.10   $125.10  
  7 purchase totals = $825.40       $894.8704   $894.87   $894.90   $895.00