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 $34.53   5.483%   $36.4233   $36.42   $36.40   $36.40  
  Purchase #2 $105.46   8.705%   $114.6403   $114.64   $114.65   $114.60  
  Purchase #3 $163.49   4.572%   $170.9648   $170.96   $170.95   $171.00  
  Purchase #4 $245.63   9.615%   $269.2473   $269.25   $269.25   $269.20  
  Purchase #5 $209.41   4.117%   $218.0314   $218.03   $218.05   $218.00  
  Purchase #6 $48.82   3.629%   $50.5917   $50.59   $50.60   $50.60  
  Purchase #7 $208.68   13.743%   $237.3589   $237.36   $237.35   $237.40  
  7 purchase totals = $1,016.02       $1,097.2577   $1,097.25   $1,097.25   $1,097.20