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 $145.76   8.227%   $157.7517   $157.75   $157.75   $157.80  
  Purchase #2 $63.57   3.430%   $65.7505   $65.75   $65.75   $65.80  
  Purchase #3 $107.38   6.110%   $113.9409   $113.94   $113.95   $113.90  
  Purchase #4 $6.64   5.806%   $7.0255   $7.03   $7.05   $7.00  
  Purchase #5 $207.43   8.629%   $225.3291   $225.33   $225.35   $225.30  
  Purchase #6 $42.86   3.810%   $44.493   $44.49   $44.50   $44.50  
  Purchase #7 $243.56   7.544%   $261.9342   $261.93   $261.95   $261.90  
  7 purchase totals = $817.20       $876.2249   $876.22   $876.30   $876.20