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 $49.70   8.455%   $53.9021   $53.90   $53.90   $53.90  
  Purchase #2 $239.57   13.242%   $271.2939   $271.29   $271.30   $271.30  
  Purchase #3 $69.57   3.716%   $72.1552   $72.16   $72.15   $72.20  
  Purchase #4 $139.44   3.622%   $144.4905   $144.49   $144.50   $144.50  
  Purchase #5 $177.56   6.453%   $189.0179   $189.02   $189.00   $189.00  
  Purchase #6 $96.95   5.130%   $101.9235   $101.92   $101.90   $101.90  
  Purchase #7 $111.58   7.571%   $120.0277   $120.03   $120.05   $120.00  
  7 purchase totals = $884.37       $952.8108   $952.81   $952.80   $952.80