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 $203.66   7.871%   $219.6901   $219.69   $219.70   $219.70  
  Purchase #2 $226.90   8.772%   $246.8037   $246.80   $246.80   $246.80  
  Purchase #3 $69.69   11.509%   $77.7106   $77.71   $77.70   $77.70  
  Purchase #4 $96.46   7.634%   $103.8238   $103.82   $103.80   $103.80  
  Purchase #5 $97.34   6.477%   $103.6447   $103.64   $103.65   $103.60  
  Purchase #6 $69.43   5.466%   $73.225   $73.23   $73.25   $73.20  
  Purchase #7 $23.28   4.612%   $24.3537   $24.35   $24.35   $24.40  
  7 purchase totals = $786.76       $849.2516   $849.24   $849.25   $849.20