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 $248.95   5.774%   $263.3244   $263.32   $263.30   $263.30  
  Purchase #2 $165.38   7.376%   $177.5784   $177.58   $177.60   $177.60  
  Purchase #3 $225.47   6.683%   $240.5382   $240.54   $240.55   $240.50  
  Purchase #4 $8.75   3.640%   $9.0685   $9.07   $9.05   $9.10  
  Purchase #5 $51.79   10.231%   $57.0886   $57.09   $57.10   $57.10  
  Purchase #6 $215.95   4.477%   $225.6181   $225.62   $225.60   $225.60  
  Purchase #7 $152.43   9.455%   $166.8423   $166.84   $166.85   $166.80  
  7 purchase totals = $1,068.72       $1,140.0585   $1,140.06   $1,140.05   $1,140.00