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 $225.58   6.302%   $239.7961   $239.80   $239.80   $239.80  
  Purchase #2 $90.84   8.548%   $98.605   $98.61   $98.60   $98.60  
  Purchase #3 $30.46   10.414%   $33.6321   $33.63   $33.65   $33.60  
  Purchase #4 $24.78   3.667%   $25.6887   $25.69   $25.70   $25.70  
  Purchase #5 $76.25   4.799%   $79.9092   $79.91   $79.90   $79.90  
  Purchase #6 $241.26   3.632%   $250.0226   $250.02   $250.00   $250.00  
  Purchase #7 $216.83   10.868%   $240.3951   $240.40   $240.40   $240.40  
  7 purchase totals = $906.00       $968.0488   $968.06   $968.05   $968.00