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 $114.73   10.298%   $126.5449   $126.54   $126.55   $126.50  
  Purchase #2 $51.95   13.382%   $58.9019   $58.90   $58.90   $58.90  
  Purchase #3 $148.79   8.749%   $161.8076   $161.81   $161.80   $161.80  
  Purchase #4 $231.91   7.145%   $248.48   $248.48   $248.50   $248.50  
  Purchase #5 $152.48   3.829%   $158.3185   $158.32   $158.30   $158.30  
  Purchase #6 $226.49   13.711%   $257.544   $257.54   $257.55   $257.50  
  Purchase #7 $72.29   6.222%   $76.7879   $76.79   $76.80   $76.80  
  7 purchase totals = $998.64       $1,088.3848   $1,088.38   $1,088.40   $1,088.30