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 $53.76   6.694%   $57.3587   $57.36   $57.35   $57.40  
  Purchase #2 $227.26   4.181%   $236.7617   $236.76   $236.75   $236.80  
  Purchase #3 $197.60   3.189%   $203.9015   $203.90   $203.90   $203.90  
  Purchase #4 $50.82   7.605%   $54.6849   $54.68   $54.70   $54.70  
  Purchase #5 $113.61   12.793%   $128.1441   $128.14   $128.15   $128.10  
  Purchase #6 $231.75   13.589%   $263.2425   $263.24   $263.25   $263.20  
  Purchase #7 $88.52   4.393%   $92.4087   $92.41   $92.40   $92.40  
  7 purchase totals = $963.32       $1,036.5021   $1,036.49   $1,036.50   $1,036.50