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 $216.94   12.671%   $244.4285   $244.43   $244.45   $244.40  
  Purchase #2 $67.96   12.231%   $76.2722   $76.27   $76.25   $76.30  
  Purchase #3 $16.86   11.356%   $18.7746   $18.77   $18.75   $18.80  
  Purchase #4 $240.83   10.537%   $266.2063   $266.21   $266.20   $266.20  
  Purchase #5 $236.26   7.791%   $254.667   $254.67   $254.65   $254.70  
  Purchase #6 $131.89   11.748%   $147.3844   $147.38   $147.40   $147.40  
  Purchase #7 $117.53   9.357%   $128.5273   $128.53   $128.55   $128.50  
  7 purchase totals = $1,028.27       $1,136.2603   $1,136.26   $1,136.25   $1,136.30