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 $227.96   3.747%   $236.5017   $236.50   $236.50   $236.50  
  Purchase #2 $22.61   4.490%   $23.6252   $23.63   $23.65   $23.60  
  Purchase #3 $246.26   8.443%   $267.0517   $267.05   $267.05   $267.10  
  Purchase #4 $64.88   8.584%   $70.4493   $70.45   $70.45   $70.40  
  Purchase #5 $142.43   10.194%   $156.9493   $156.95   $156.95   $156.90  
  Purchase #6 $225.90   13.459%   $256.3039   $256.30   $256.30   $256.30  
  Purchase #7 $39.54   3.352%   $40.8654   $40.87   $40.85   $40.90  
  7 purchase totals = $969.58       $1,051.7465   $1,051.75   $1,051.75   $1,051.70