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 $250.66   7.569%   $269.6325   $269.63   $269.65   $269.60  
  Purchase #2 $66.49   4.855%   $69.7181   $69.72   $69.70   $69.70  
  Purchase #3 $5.98   6.747%   $6.3835   $6.38   $6.40   $6.40  
  Purchase #4 $42.51   9.578%   $46.5816   $46.58   $46.60   $46.60  
  Purchase #5 $225.66   3.852%   $234.3524   $234.35   $234.35   $234.40  
  Purchase #6 $216.31   8.239%   $234.1318   $234.13   $234.15   $234.10  
  Purchase #7 $22.44   9.152%   $24.4937   $24.49   $24.50   $24.50  
  7 purchase totals = $830.05       $885.2936   $885.28   $885.35   $885.30