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 $165.50   11.755%   $184.9545   $184.95   $184.95   $185.00  
  Purchase #2 $242.99   6.476%   $258.726   $258.73   $258.75   $258.70  
  Purchase #3 $207.85   12.773%   $234.3987   $234.40   $234.40   $234.40  
  Purchase #4 $226.40   5.178%   $238.123   $238.12   $238.10   $238.10  
  Purchase #5 $190.94   3.388%   $197.409   $197.41   $197.40   $197.40  
  Purchase #6 $190.46   7.724%   $205.1711   $205.17   $205.15   $205.20  
  Purchase #7 $189.60   9.669%   $207.9324   $207.93   $207.95   $207.90  
  7 purchase totals = $1,413.74       $1,526.7147   $1,526.71   $1,526.70   $1,526.70