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 $85.51   10.371%   $94.3782   $94.38   $94.40   $94.40  
  Purchase #2 $107.76   7.562%   $115.9088   $115.91   $115.90   $115.90  
  Purchase #3 $196.87   13.764%   $223.9672   $223.97   $223.95   $224.00  
  Purchase #4 $103.89   13.594%   $118.0128   $118.01   $118.00   $118.00  
  Purchase #5 $124.31   7.462%   $133.586   $133.59   $133.60   $133.60  
  Purchase #6 $163.42   3.365%   $168.9191   $168.92   $168.90   $168.90  
  Purchase #7 $215.67   4.291%   $224.9244   $224.92   $224.90   $224.90  
  7 purchase totals = $997.43       $1,079.6965   $1,079.70   $1,079.65   $1,079.70