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 $231.35   6.747%   $246.9592   $246.96   $246.95   $247.00  
  Purchase #2 $233.79   10.290%   $257.847   $257.85   $257.85   $257.80  
  Purchase #3 $154.41   9.309%   $168.784   $168.78   $168.80   $168.80  
  Purchase #4 $183.46   7.784%   $197.7405   $197.74   $197.75   $197.70  
  Purchase #5 $68.67   7.361%   $73.7248   $73.72   $73.70   $73.70  
  Purchase #6 $164.30   3.548%   $170.1294   $170.13   $170.15   $170.10  
  Purchase #7 $117.62   11.104%   $130.6805   $130.68   $130.70   $130.70  
  7 purchase totals = $1,153.60       $1,245.8654   $1,245.86   $1,245.90   $1,245.80