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 $78.58   10.702%   $86.9896   $86.99   $87.00   $87.00  
  Purchase #2 $214.99   5.546%   $226.9133   $226.91   $226.90   $226.90  
  Purchase #3 $172.30   5.856%   $182.3899   $182.39   $182.40   $182.40  
  Purchase #4 $81.44   7.213%   $87.3143   $87.31   $87.30   $87.30  
  Purchase #5 $171.25   8.217%   $185.3216   $185.32   $185.30   $185.30  
  Purchase #6 $241.65   7.684%   $260.2184   $260.22   $260.20   $260.20  
  Purchase #7 $133.42   13.182%   $151.0074   $151.01   $151.00   $151.00  
  7 purchase totals = $1,093.63       $1,180.1545   $1,180.15   $1,180.10   $1,180.10