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	$244.97	13.670%	$278.4574	$278.46	$278.45	$278.50
Purchase #2	$57.76	3.522%	$59.7943	$59.79	$59.80	$59.80
Purchase #3	$85.61	12.702%	$96.4842	$96.48	$96.50	$96.50
Purchase #4	$83.54	6.592%	$89.047	$89.05	$89.05	$89.00
Purchase #5	$63.70	4.653%	$66.664	$66.66	$66.65	$66.70
Purchase #6	$50.76	7.729%	$54.6832	$54.68	$54.70	$54.70
Purchase #7	$243.71	12.684%	$274.6222	$274.62	$274.60	$274.60
7 purchase totals =	$830.05		$919.7523	$919.74	$919.75	$919.80