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 $238.83   3.644%   $247.533   $247.53   $247.55   $247.50  
  Purchase #2 $195.57   10.233%   $215.5827   $215.58   $215.60   $215.60  
  Purchase #3 $24.82   8.649%   $26.9667   $26.97   $26.95   $27.00  
  Purchase #4 $167.77   5.795%   $177.4923   $177.49   $177.50   $177.50  
  Purchase #5 $154.75   8.570%   $168.0121   $168.01   $168.00   $168.00  
  Purchase #6 $209.57   7.767%   $225.8473   $225.85   $225.85   $225.80  
  Purchase #7 $144.64   6.866%   $154.571   $154.57   $154.55   $154.60  
  7 purchase totals = $1,135.95       $1,216.0051   $1,216.00   $1,216.00   $1,216.00