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 $246.84   7.597%   $265.5924   $265.59   $265.60   $265.60  
  Purchase #2 $114.77   13.660%   $130.4476   $130.45   $130.45   $130.40  
  Purchase #3 $151.71   6.747%   $161.9459   $161.95   $161.95   $161.90  
  Purchase #4 $5.51   7.439%   $5.9199   $5.92   $5.90   $5.90  
  Purchase #5 $240.69   11.125%   $267.4668   $267.47   $267.45   $267.50  
  Purchase #6 $208.78   11.425%   $232.6331   $232.63   $232.65   $232.60  
  Purchase #7 $143.68   12.457%   $161.5782   $161.58   $161.60   $161.60  
  7 purchase totals = $1,111.98       $1,225.5839   $1,225.59   $1,225.60   $1,225.50