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 $76.42   3.725%   $79.2666   $79.27   $79.25   $79.30  
  Purchase #2 $222.56   10.375%   $245.6506   $245.65   $245.65   $245.70  
  Purchase #3 $233.69   13.246%   $264.6446   $264.64   $264.65   $264.60  
  Purchase #4 $235.73   11.237%   $262.219   $262.22   $262.20   $262.20  
  Purchase #5 $65.49   12.377%   $73.5957   $73.60   $73.60   $73.60  
  Purchase #6 $125.94   6.804%   $134.509   $134.51   $134.50   $134.50  
  Purchase #7 $126.34   7.545%   $135.8724   $135.87   $135.85   $135.90  
  7 purchase totals = $1,086.17       $1,195.7579   $1,195.76   $1,195.70   $1,195.80