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 $243.44   13.335%   $275.9027   $275.90   $275.90   $275.90  
  Purchase #2 $69.97   8.178%   $75.6921   $75.69   $75.70   $75.70  
  Purchase #3 $23.69   10.749%   $26.2364   $26.24   $26.25   $26.20  
  Purchase #4 $21.55   12.618%   $24.2692   $24.27   $24.25   $24.30  
  Purchase #5 $155.45   8.174%   $168.1565   $168.16   $168.15   $168.20  
  Purchase #6 $140.65   12.149%   $157.7376   $157.74   $157.75   $157.70  
  Purchase #7 $23.52   3.352%   $24.3084   $24.31   $24.30   $24.30  
  7 purchase totals = $678.27       $752.3029   $752.31   $752.30   $752.30