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 $198.26   11.856%   $221.7657   $221.77   $221.75   $221.80  
  Purchase #2 $234.44   5.293%   $246.8489   $246.85   $246.85   $246.80  
  Purchase #3 $64.81   13.739%   $73.7142   $73.71   $73.70   $73.70  
  Purchase #4 $60.81   10.768%   $67.358   $67.36   $67.35   $67.40  
  Purchase #5 $249.52   12.855%   $281.5958   $281.60   $281.60   $281.60  
  Purchase #6 $239.50   13.435%   $271.6768   $271.68   $271.70   $271.70  
  Purchase #7 $186.59   8.664%   $202.7562   $202.76   $202.75   $202.80  
  7 purchase totals = $1,233.93       $1,365.7156   $1,365.73   $1,365.70   $1,365.80