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 $59.84   11.726%   $66.8568   $66.86   $66.85   $66.90  
  Purchase #2 $172.79   7.532%   $185.8045   $185.80   $185.80   $185.80  
  Purchase #3 $227.81   3.435%   $235.6353   $235.64   $235.65   $235.60  
  Purchase #4 $97.62   4.759%   $102.2657   $102.27   $102.25   $102.30  
  Purchase #5 $167.34   8.816%   $182.0927   $182.09   $182.10   $182.10  
  Purchase #6 $164.92   4.391%   $172.1616   $172.16   $172.15   $172.20  
  Purchase #7 $214.81   8.771%   $233.651   $233.65   $233.65   $233.70  
  7 purchase totals = $1,105.13       $1,178.4676   $1,178.47   $1,178.45   $1,178.60