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 $186.69   7.178%   $200.0906   $200.09   $200.10   $200.10  
  Purchase #2 $127.34   3.608%   $131.9344   $131.93   $131.95   $131.90  
  Purchase #3 $12.69   11.273%   $14.1205   $14.12   $14.10   $14.10  
  Purchase #4 $162.36   8.388%   $175.9788   $175.98   $176.00   $176.00  
  Purchase #5 $206.65   13.366%   $234.2708   $234.27   $234.25   $234.30  
  Purchase #6 $244.70   11.526%   $272.9041   $272.90   $272.90   $272.90  
  Purchase #7 $86.98   10.410%   $96.0346   $96.03   $96.05   $96.00  
  7 purchase totals = $1,027.41       $1,125.3338   $1,125.32   $1,125.35   $1,125.30