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 $69.85   11.144%   $77.6341   $77.63   $77.65   $77.60  
  Purchase #2 $205.48   6.208%   $218.2362   $218.24   $218.25   $218.20  
  Purchase #3 $245.76   8.490%   $266.625   $266.63   $266.65   $266.60  
  Purchase #4 $88.56   8.848%   $96.3958   $96.40   $96.40   $96.40  
  Purchase #5 $111.83   7.238%   $119.9243   $119.92   $119.90   $119.90  
  Purchase #6 $146.99   3.583%   $152.2567   $152.26   $152.25   $152.30  
  Purchase #7 $66.99   9.414%   $73.2964   $73.30   $73.30   $73.30  
  7 purchase totals = $935.46       $1,004.3685   $1,004.38   $1,004.40   $1,004.30