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 $151.48   6.458%   $161.2626   $161.26   $161.25   $161.30  
  Purchase #2 $242.63   11.145%   $269.6711   $269.67   $269.65   $269.70  
  Purchase #3 $150.59   5.247%   $158.4915   $158.49   $158.50   $158.50  
  Purchase #4 $225.97   5.284%   $237.9103   $237.91   $237.90   $237.90  
  Purchase #5 $194.44   10.527%   $214.9087   $214.91   $214.90   $214.90  
  Purchase #6 $221.25   13.738%   $251.6453   $251.65   $251.65   $251.60  
  Purchase #7 $10.88   3.415%   $11.2516   $11.25   $11.25   $11.30  
  7 purchase totals = $1,197.24       $1,305.1411   $1,305.14   $1,305.10   $1,305.20