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 $161.46   4.422%   $168.5998   $168.60   $168.60   $168.60  
  Purchase #2 $24.55   4.167%   $25.573   $25.57   $25.55   $25.60  
  Purchase #3 $68.97   10.547%   $76.2443   $76.24   $76.25   $76.20  
  Purchase #4 $125.28   5.168%   $131.7545   $131.75   $131.75   $131.80  
  Purchase #5 $214.36   12.484%   $241.1207   $241.12   $241.10   $241.10  
  Purchase #6 $182.35   9.642%   $199.9322   $199.93   $199.95   $199.90  
  Purchase #7 $208.56   8.329%   $225.931   $225.93   $225.95   $225.90  
  7 purchase totals = $985.53       $1,069.1555   $1,069.14   $1,069.15   $1,069.10