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 $189.70   13.229%   $214.7954   $214.80   $214.80   $214.80  
  Purchase #2 $175.92   11.337%   $195.8641   $195.86   $195.85   $195.90  
  Purchase #3 $192.39   11.197%   $213.9319   $213.93   $213.95   $213.90  
  Purchase #4 $226.98   7.160%   $243.2318   $243.23   $243.25   $243.20  
  Purchase #5 $55.97   9.481%   $61.2765   $61.28   $61.30   $61.30  
  Purchase #6 $183.28   4.664%   $191.8282   $191.83   $191.85   $191.80  
  Purchase #7 $209.66   8.854%   $228.2233   $228.22   $228.20   $228.20  
  7 purchase totals = $1,233.90       $1,349.1512   $1,349.15   $1,349.20   $1,349.10