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 $66.65   10.324%   $73.5309   $73.53   $73.55   $73.50  
  Purchase #2 $185.56   12.289%   $208.3635   $208.36   $208.35   $208.40  
  Purchase #3 $196.40   11.167%   $218.332   $218.33   $218.35   $218.30  
  Purchase #4 $22.51   4.663%   $23.5596   $23.56   $23.55   $23.60  
  Purchase #5 $27.50   12.350%   $30.8963   $30.90   $30.90   $30.90  
  Purchase #6 $239.26   4.500%   $250.0267   $250.03   $250.05   $250.00  
  Purchase #7 $57.91   7.658%   $62.3447   $62.34   $62.35   $62.30  
  7 purchase totals = $795.79       $867.0537   $867.05   $867.10   $867.00