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 $60.92   5.347%   $64.1774   $64.18   $64.20   $64.20  
  Purchase #2 $97.95   4.832%   $102.6829   $102.68   $102.70   $102.70  
  Purchase #3 $130.79   4.856%   $137.1412   $137.14   $137.15   $137.10  
  Purchase #4 $158.81   7.234%   $170.2983   $170.30   $170.30   $170.30  
  Purchase #5 $80.50   6.246%   $85.528   $85.53   $85.55   $85.50  
  Purchase #6 $34.59   3.717%   $35.8757   $35.88   $35.90   $35.90  
  Purchase #7 $118.64   7.402%   $127.4217   $127.42   $127.40   $127.40  
  7 purchase totals = $682.20       $723.1252   $723.13   $723.20   $723.10