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 $39.73   12.115%   $44.5433   $44.54   $44.55   $44.50  
  Purchase #2 $168.73   9.438%   $184.6547   $184.65   $184.65   $184.70  
  Purchase #3 $24.74   4.605%   $25.8793   $25.88   $25.90   $25.90  
  Purchase #4 $225.60   4.680%   $236.1581   $236.16   $236.15   $236.20  
  Purchase #5 $143.83   3.237%   $148.4858   $148.49   $148.50   $148.50  
  Purchase #6 $49.89   4.233%   $52.0018   $52.00   $52.00   $52.00  
  Purchase #7 $182.58   5.672%   $192.9359   $192.94   $192.95   $192.90  
  7 purchase totals = $835.10       $884.6589   $884.66   $884.70   $884.70