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 $245.32   11.568%   $273.6986   $273.70   $273.70   $273.70  
  Purchase #2 $126.29   9.151%   $137.8468   $137.85   $137.85   $137.80  
  Purchase #3 $230.34   10.683%   $254.9472   $254.95   $254.95   $254.90  
  Purchase #4 $154.37   8.327%   $167.2244   $167.22   $167.20   $167.20  
  Purchase #5 $171.40   7.671%   $184.5481   $184.55   $184.55   $184.50  
  Purchase #6 $71.27   7.724%   $76.7749   $76.77   $76.75   $76.80  
  Purchase #7 $114.82   3.808%   $119.1923   $119.19   $119.20   $119.20  
  7 purchase totals = $1,113.81       $1,214.2323   $1,214.23   $1,214.20   $1,214.10