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 $64.59   8.201%   $69.887   $69.89   $69.90   $69.90  
  Purchase #2 $48.39   13.175%   $54.7654   $54.77   $54.75   $54.80  
  Purchase #3 $29.69   11.793%   $33.1913   $33.19   $33.20   $33.20  
  Purchase #4 $227.73   9.246%   $248.7859   $248.79   $248.80   $248.80  
  Purchase #5 $6.28   5.303%   $6.613   $6.61   $6.60   $6.60  
  Purchase #6 $126.68   12.477%   $142.4859   $142.49   $142.50   $142.50  
  Purchase #7 $242.60   12.791%   $273.631   $273.63   $273.65   $273.60  
  7 purchase totals = $745.96       $829.3595   $829.37   $829.40   $829.40