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 $151.48   7.443%   $162.7547   $162.75   $162.75   $162.80  
  Purchase #2 $239.30   11.281%   $266.2954   $266.30   $266.30   $266.30  
  Purchase #3 $239.28   12.835%   $269.9916   $269.99   $270.00   $270.00  
  Purchase #4 $173.88   13.826%   $197.9206   $197.92   $197.90   $197.90  
  Purchase #5 $75.33   11.751%   $84.182   $84.18   $84.20   $84.20  
  Purchase #6 $242.34   3.521%   $250.8728   $250.87   $250.85   $250.90  
  Purchase #7 $124.98   11.828%   $139.7626   $139.76   $139.75   $139.80  
  7 purchase totals = $1,246.59       $1,371.7797   $1,371.77   $1,371.75   $1,371.90