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 $62.44   3.246%   $64.4668   $64.47   $64.45   $64.50  
  Purchase #2 $236.40   5.183%   $248.6526   $248.65   $248.65   $248.70  
  Purchase #3 $191.26   13.760%   $217.5774   $217.58   $217.60   $217.60  
  Purchase #4 $34.31   9.212%   $37.4706   $37.47   $37.45   $37.50  
  Purchase #5 $158.77   11.819%   $177.535   $177.54   $177.55   $177.50  
  Purchase #6 $129.92   11.489%   $144.8465   $144.85   $144.85   $144.80  
  Purchase #7 $19.97   5.498%   $21.068   $21.07   $21.05   $21.10  
  7 purchase totals = $833.07       $911.6169   $911.63   $911.60   $911.70