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 $246.54   9.210%   $269.2463   $269.25   $269.25   $269.20  
  Purchase #2 $84.57   8.304%   $91.5927   $91.59   $91.60   $91.60  
  Purchase #3 $145.90   8.423%   $158.1892   $158.19   $158.20   $158.20  
  Purchase #4 $24.32   6.281%   $25.8475   $25.85   $25.85   $25.80  
  Purchase #5 $92.28   10.163%   $101.6584   $101.66   $101.65   $101.70  
  Purchase #6 $14.32   7.203%   $15.3515   $15.35   $15.35   $15.40  
  Purchase #7 $250.66   4.321%   $261.491   $261.49   $261.50   $261.50  
  7 purchase totals = $858.59       $923.3766   $923.38   $923.40   $923.40