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 $227.39   5.402%   $239.6736   $239.67   $239.65   $239.70  
  Purchase #2 $92.89   5.598%   $98.09   $98.09   $98.10   $98.10  
  Purchase #3 $90.90   5.783%   $96.1567   $96.16   $96.15   $96.20  
  Purchase #4 $236.86   12.595%   $266.6925   $266.69   $266.70   $266.70  
  Purchase #5 $21.68   5.584%   $22.8906   $22.89   $22.90   $22.90  
  Purchase #6 $207.55   7.636%   $223.3985   $223.40   $223.40   $223.40  
  Purchase #7 $57.94   4.849%   $60.7495   $60.75   $60.75   $60.70  
  7 purchase totals = $935.21       $1,007.6514   $1,007.65   $1,007.65   $1,007.70