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 $75.87   13.865%   $86.3894   $86.39   $86.40   $86.40  
  Purchase #2 $214.28   10.151%   $236.0316   $236.03   $236.05   $236.00  
  Purchase #3 $241.47   6.135%   $256.2842   $256.28   $256.30   $256.30  
  Purchase #4 $140.61   7.575%   $151.2612   $151.26   $151.25   $151.30  
  Purchase #5 $226.68   6.778%   $242.0444   $242.04   $242.05   $242.00  
  Purchase #6 $65.88   13.111%   $74.5175   $74.52   $74.50   $74.50  
  Purchase #7 $157.51   13.548%   $178.8495   $178.85   $178.85   $178.80  
  7 purchase totals = $1,122.30       $1,225.3778   $1,225.37   $1,225.40   $1,225.30