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 $76.91   3.838%   $79.8618   $79.86   $79.85   $79.90  
  Purchase #2 $53.52   5.104%   $56.2517   $56.25   $56.25   $56.30  
  Purchase #3 $111.60   12.219%   $125.2364   $125.24   $125.25   $125.20  
  Purchase #4 $218.93   11.547%   $244.2098   $244.21   $244.20   $244.20  
  Purchase #5 $207.74   9.233%   $226.9206   $226.92   $226.90   $226.90  
  Purchase #6 $83.97   3.127%   $86.5957   $86.60   $86.60   $86.60  
  Purchase #7 $73.54   11.402%   $81.925   $81.93   $81.95   $81.90  
  7 purchase totals = $826.21       $901.0010   $901.01   $901.00   $901.00