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 $104.73   10.472%   $115.6973   $115.70   $115.70   $115.70  
  Purchase #2 $8.81   9.847%   $9.6775   $9.68   $9.70   $9.70  
  Purchase #3 $26.36   3.312%   $27.233   $27.23   $27.25   $27.20  
  Purchase #4 $188.39   9.763%   $206.7825   $206.78   $206.80   $206.80  
  Purchase #5 $166.86   9.632%   $182.932   $182.93   $182.95   $182.90  
  Purchase #6 $122.75   9.246%   $134.0995   $134.10   $134.10   $134.10  
  Purchase #7 $209.63   4.267%   $218.5749   $218.57   $218.55   $218.60  
  7 purchase totals = $827.53       $894.9967   $894.99   $895.05   $895.00