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 $22.38   4.617%   $23.4133   $23.41   $23.40   $23.40  
  Purchase #2 $214.44   10.461%   $236.8726   $236.87   $236.85   $236.90  
  Purchase #3 $162.31   9.259%   $177.3383   $177.34   $177.35   $177.30  
  Purchase #4 $82.27   6.113%   $87.2992   $87.30   $87.30   $87.30  
  Purchase #5 $158.37   6.213%   $168.2095   $168.21   $168.20   $168.20  
  Purchase #6 $241.31   9.484%   $264.1958   $264.20   $264.20   $264.20  
  Purchase #7 $48.95   9.745%   $53.7202   $53.72   $53.70   $53.70  
  7 purchase totals = $930.03       $1,011.0489   $1,011.05   $1,011.00   $1,011.00