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 $55.61   6.164%   $59.0378   $59.04   $59.05   $59.00  
  Purchase #2 $92.28   10.249%   $101.7378   $101.74   $101.75   $101.70  
  Purchase #3 $96.36   4.369%   $100.57   $100.57   $100.55   $100.60  
  Purchase #4 $108.41   13.282%   $122.809   $122.81   $122.80   $122.80  
  Purchase #5 $118.64   5.292%   $124.9184   $124.92   $124.90   $124.90  
  Purchase #6 $184.78   6.845%   $197.4282   $197.43   $197.45   $197.40  
  Purchase #7 $60.49   10.602%   $66.9031   $66.90   $66.90   $66.90  
  7 purchase totals = $716.57       $773.4043   $773.41   $773.40   $773.30