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 $242.48   10.522%   $267.9937   $267.99   $268.00   $268.00  
  Purchase #2 $152.80   9.274%   $166.9707   $166.97   $166.95   $167.00  
  Purchase #3 $55.55   7.574%   $59.7574   $59.76   $59.75   $59.80  
  Purchase #4 $86.39   6.750%   $92.2213   $92.22   $92.20   $92.20  
  Purchase #5 $217.71   4.317%   $227.1085   $227.11   $227.10   $227.10  
  Purchase #6 $38.69   4.662%   $40.4937   $40.49   $40.50   $40.50  
  Purchase #7 $27.59   10.819%   $30.575   $30.58   $30.60   $30.60  
  7 purchase totals = $821.21       $885.1203   $885.12   $885.10   $885.20