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 $79.95   10.249%   $88.1441   $88.14   $88.15   $88.10  
  Purchase #2 $40.90   5.602%   $43.1912   $43.19   $43.20   $43.20  
  Purchase #3 $43.51   11.543%   $48.5324   $48.53   $48.55   $48.50  
  Purchase #4 $230.55   4.850%   $241.7317   $241.73   $241.75   $241.70  
  Purchase #5 $224.67   13.557%   $255.1285   $255.13   $255.15   $255.10  
  Purchase #6 $245.99   10.332%   $271.4057   $271.41   $271.40   $271.40  
  Purchase #7 $194.92   11.164%   $216.6809   $216.68   $216.70   $216.70  
  7 purchase totals = $1,060.49       $1,164.8145   $1,164.81   $1,164.90   $1,164.70