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 $67.39   5.648%   $71.1962   $71.20   $71.20   $71.20  
  Purchase #2 $182.35   13.210%   $206.4384   $206.44   $206.45   $206.40  
  Purchase #3 $20.40   4.307%   $21.2786   $21.28   $21.30   $21.30  
  Purchase #4 $43.99   6.393%   $46.8023   $46.80   $46.80   $46.80  
  Purchase #5 $140.56   10.589%   $155.4439   $155.44   $155.45   $155.40  
  Purchase #6 $182.38   8.495%   $197.8732   $197.87   $197.85   $197.90  
  Purchase #7 $22.49   10.822%   $24.9239   $24.92   $24.90   $24.90  
  7 purchase totals = $659.56       $723.9565   $723.95   $723.95   $723.90