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 $56.87   8.242%   $61.5572   $61.56   $61.55   $61.60  
  Purchase #2 $8.38   13.826%   $9.5386   $9.54   $9.55   $9.50  
  Purchase #3 $25.27   9.310%   $27.6226   $27.62   $27.60   $27.60  
  Purchase #4 $111.39   8.659%   $121.0353   $121.04   $121.05   $121.00  
  Purchase #5 $241.76   3.184%   $249.4576   $249.46   $249.45   $249.50  
  Purchase #6 $177.57   8.842%   $193.2707   $193.27   $193.25   $193.30  
  Purchase #7 $101.73   10.839%   $112.7565   $112.76   $112.75   $112.80  
  7 purchase totals = $722.97       $775.2385   $775.25   $775.20   $775.30