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 $199.53   13.492%   $226.4506   $226.45   $226.45   $226.50  
  Purchase #2 $220.33   10.427%   $243.3038   $243.30   $243.30   $243.30  
  Purchase #3 $118.29   4.857%   $124.0353   $124.04   $124.05   $124.00  
  Purchase #4 $206.32   4.430%   $215.46   $215.46   $215.45   $215.50  
  Purchase #5 $61.37   13.451%   $69.6249   $69.62   $69.60   $69.60  
  Purchase #6 $216.63   10.108%   $238.527   $238.53   $238.55   $238.50  
  Purchase #7 $239.91   13.491%   $272.2763   $272.28   $272.30   $272.30  
  7 purchase totals = $1,262.38       $1,389.6779   $1,389.68   $1,389.70   $1,389.70