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 $247.59   6.871%   $264.6019   $264.60   $264.60   $264.60  
  Purchase #2 $169.41   13.738%   $192.6835   $192.68   $192.70   $192.70  
  Purchase #3 $80.51   3.785%   $83.5573   $83.56   $83.55   $83.60  
  Purchase #4 $199.37   9.714%   $218.7368   $218.74   $218.75   $218.70  
  Purchase #5 $178.32   5.529%   $188.1793   $188.18   $188.20   $188.20  
  Purchase #6 $210.71   7.853%   $227.2571   $227.26   $227.25   $227.30  
  Purchase #7 $117.43   10.196%   $129.4032   $129.40   $129.40   $129.40  
  7 purchase totals = $1,203.34       $1,304.4191   $1,304.42   $1,304.45   $1,304.50