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 $13.76   8.478%   $14.9266   $14.93   $14.95   $14.90  
  Purchase #2 $60.68   4.813%   $63.6005   $63.60   $63.60   $63.60  
  Purchase #3 $27.60   9.770%   $30.2965   $30.30   $30.30   $30.30  
  Purchase #4 $77.39   13.177%   $87.5877   $87.59   $87.60   $87.60  
  Purchase #5 $184.42   4.466%   $192.6562   $192.66   $192.65   $192.70  
  Purchase #6 $30.63   7.451%   $32.9122   $32.91   $32.90   $32.90  
  Purchase #7 $75.58   8.808%   $82.2371   $82.24   $82.25   $82.20  
  7 purchase totals = $470.06       $504.2168   $504.23   $504.25   $504.20