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 $194.91   6.652%   $207.8754   $207.88   $207.90   $207.90  
  Purchase #2 $88.76   6.863%   $94.8516   $94.85   $94.85   $94.90  
  Purchase #3 $236.30   9.832%   $259.533   $259.53   $259.55   $259.50  
  Purchase #4 $25.45   7.741%   $27.4201   $27.42   $27.40   $27.40  
  Purchase #5 $189.31   4.501%   $197.8308   $197.83   $197.85   $197.80  
  Purchase #6 $120.25   10.808%   $133.2466   $133.25   $133.25   $133.20  
  Purchase #7 $95.50   5.859%   $101.0953   $101.10   $101.10   $101.10  
  7 purchase totals = $950.48       $1,021.8528   $1,021.86   $1,021.90   $1,021.80