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 $238.49   3.828%   $247.6194   $247.62   $247.60   $247.60  
  Purchase #2 $172.75   5.828%   $182.8179   $182.82   $182.80   $182.80  
  Purchase #3 $248.59   7.509%   $267.2566   $267.26   $267.25   $267.30  
  Purchase #4 $40.69   10.435%   $44.936   $44.94   $44.95   $44.90  
  Purchase #5 $202.28   12.490%   $227.5448   $227.54   $227.55   $227.50  
  Purchase #6 $171.46   7.264%   $183.9149   $183.91   $183.90   $183.90  
  Purchase #7 $168.94   8.241%   $182.8623   $182.86   $182.85   $182.90  
  7 purchase totals = $1,243.20       $1,336.9519   $1,336.95   $1,336.90   $1,336.90