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 $155.48   8.541%   $168.7595   $168.76   $168.75   $168.80  
  Purchase #2 $171.41   12.416%   $192.6923   $192.69   $192.70   $192.70  
  Purchase #3 $132.37   8.230%   $143.2641   $143.26   $143.25   $143.30  
  Purchase #4 $170.95   8.618%   $185.6825   $185.68   $185.70   $185.70  
  Purchase #5 $47.47   5.611%   $50.1335   $50.13   $50.15   $50.10  
  Purchase #6 $158.72   4.461%   $165.8005   $165.80   $165.80   $165.80  
  Purchase #7 $52.59   5.420%   $55.4404   $55.44   $55.45   $55.40  
  7 purchase totals = $888.99       $961.7728   $961.76   $961.80   $961.80