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	$250.42	3.748%	$259.8057	$259.81	$259.80	$259.80
Purchase #2	$88.54	11.154%	$98.4158	$98.42	$98.40	$98.40
Purchase #3	$157.81	7.472%	$169.6016	$169.60	$169.60	$169.60
Purchase #4	$211.55	3.728%	$219.4366	$219.44	$219.45	$219.40
Purchase #5	$138.76	5.769%	$146.7651	$146.77	$146.75	$146.80
Purchase #6	$43.77	4.255%	$45.6324	$45.63	$45.65	$45.60
Purchase #7	$53.82	10.330%	$59.3796	$59.38	$59.40	$59.40
7 purchase totals =	$944.67		$999.0368	$999.05	$999.05	$999.00