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	$106.55	12.190%	$119.5384	$119.54	$119.55	$119.50
Purchase #2	$29.38	6.235%	$31.2118	$31.21	$31.20	$31.20
Purchase #3	$242.47	12.616%	$273.06	$273.06	$273.05	$273.10
Purchase #4	$141.83	3.446%	$146.7175	$146.72	$146.70	$146.70
Purchase #5	$75.38	13.847%	$85.8179	$85.82	$85.80	$85.80
Purchase #6	$126.80	13.834%	$144.3415	$144.34	$144.35	$144.30
Purchase #7	$13.26	11.482%	$14.7825	$14.78	$14.80	$14.80
7 purchase totals =	$735.67		$815.4696	$815.47	$815.45	$815.40