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 $204.90   10.151%   $225.6994   $225.70   $225.70   $225.70  
  Purchase #2 $172.44   7.846%   $185.9696   $185.97   $185.95   $186.00  
  Purchase #3 $211.86   13.173%   $239.7683   $239.77   $239.75   $239.80  
  Purchase #4 $72.46   6.103%   $76.8822   $76.88   $76.90   $76.90  
  Purchase #5 $239.49   3.561%   $248.0182   $248.02   $248.00   $248.00  
  Purchase #6 $196.50   9.273%   $214.7214   $214.72   $214.70   $214.70  
  Purchase #7 $164.29   5.720%   $173.6874   $173.69   $173.70   $173.70  
  7 purchase totals = $1,261.94       $1,364.7465   $1,364.75   $1,364.70   $1,364.80