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	$198.33	3.225%	$204.7261	$204.73	$204.75	$204.70
Purchase #2	$158.89	8.786%	$172.8501	$172.85	$172.85	$172.90
Purchase #3	$46.77	13.521%	$53.0938	$53.09	$53.10	$53.10
Purchase #4	$241.60	5.470%	$254.8155	$254.82	$254.80	$254.80
Purchase #5	$70.36	3.234%	$72.6354	$72.64	$72.65	$72.60
Purchase #6	$49.35	12.358%	$55.4487	$55.45	$55.45	$55.40
Purchase #7	$157.91	13.593%	$179.3747	$179.37	$179.35	$179.40
7 purchase totals =	$923.21		$992.9443	$992.95	$992.95	$992.90