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 $38.34   13.244%   $43.4177   $43.42   $43.40   $43.40  
  Purchase #2 $168.68   7.441%   $181.2315   $181.23   $181.25   $181.20  
  Purchase #3 $84.29   3.859%   $87.5428   $87.54   $87.55   $87.50  
  Purchase #4 $46.90   6.116%   $49.7684   $49.77   $49.75   $49.80  
  Purchase #5 $159.93   11.421%   $178.1956   $178.20   $178.20   $178.20  
  Purchase #6 $11.28   5.255%   $11.8728   $11.87   $11.85   $11.90  
  Purchase #7 $205.47   10.584%   $227.2169   $227.22   $227.20   $227.20  
  7 purchase totals = $714.89       $779.2457   $779.25   $779.20   $779.20