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 $206.38   13.233%   $233.6903   $233.69   $233.70   $233.70  
  Purchase #2 $176.52   5.513%   $186.2515   $186.25   $186.25   $186.30  
  Purchase #3 $83.74   13.451%   $95.0039   $95.00   $95.00   $95.00  
  Purchase #4 $231.91   5.532%   $244.7393   $244.74   $244.75   $244.70  
  Purchase #5 $13.72   4.730%   $14.369   $14.37   $14.35   $14.40  
  Purchase #6 $244.91   6.790%   $261.5394   $261.54   $261.55   $261.50  
  Purchase #7 $215.90   7.534%   $232.1659   $232.17   $232.15   $232.20  
  7 purchase totals = $1,173.08       $1,267.7593   $1,267.76   $1,267.75   $1,267.80