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 $223.32   11.410%   $248.8008   $248.80   $248.80   $248.80  
  Purchase #2 $113.63   7.246%   $121.8636   $121.86   $121.85   $121.90  
  Purchase #3 $246.56   3.676%   $255.6235   $255.62   $255.60   $255.60  
  Purchase #4 $176.72   12.556%   $198.909   $198.91   $198.90   $198.90  
  Purchase #5 $111.69   5.223%   $117.5236   $117.52   $117.50   $117.50  
  Purchase #6 $56.74   7.149%   $60.7963   $60.80   $60.80   $60.80  
  Purchase #7 $233.27   12.582%   $262.62   $262.62   $262.60   $262.60  
  7 purchase totals = $1,161.93       $1,266.1368   $1,266.13   $1,266.05   $1,266.10