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 $115.81   3.496%   $119.8587   $119.86   $119.85   $119.90  
  Purchase #2 $75.44   13.209%   $85.4049   $85.40   $85.40   $85.40  
  Purchase #3 $75.90   9.128%   $82.8282   $82.83   $82.85   $82.80  
  Purchase #4 $132.70   3.146%   $136.8747   $136.87   $136.85   $136.90  
  Purchase #5 $161.91   3.454%   $167.5024   $167.50   $167.50   $167.50  
  Purchase #6 $148.71   3.520%   $153.9446   $153.94   $153.95   $153.90  
  Purchase #7 $163.85   6.371%   $174.2889   $174.29   $174.30   $174.30  
  7 purchase totals = $874.32       $920.7024   $920.69   $920.70   $920.70