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 $56.47   12.536%   $63.5491   $63.55   $63.55   $63.50  
  Purchase #2 $100.58   4.776%   $105.3837   $105.38   $105.40   $105.40  
  Purchase #3 $163.78   3.385%   $169.324   $169.32   $169.30   $169.30  
  Purchase #4 $51.34   6.472%   $54.6627   $54.66   $54.65   $54.70  
  Purchase #5 $110.60   4.828%   $115.9398   $115.94   $115.95   $115.90  
  Purchase #6 $156.97   12.681%   $176.8754   $176.88   $176.90   $176.90  
  Purchase #7 $233.46   12.511%   $262.6682   $262.67   $262.65   $262.70  
  7 purchase totals = $873.20       $948.4029   $948.40   $948.40   $948.40