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	$28.25	13.476%	$32.057	$32.06	$32.05	$32.10
Purchase #2	$212.35	7.451%	$228.1722	$228.17	$228.15	$228.20
Purchase #3	$27.58	4.202%	$28.7389	$28.74	$28.75	$28.70
Purchase #4	$158.78	13.715%	$180.5567	$180.56	$180.55	$180.60
Purchase #5	$214.91	13.243%	$243.3705	$243.37	$243.35	$243.40
Purchase #6	$96.27	4.827%	$100.917	$100.92	$100.90	$100.90
Purchase #7	$81.32	6.859%	$86.8977	$86.90	$86.90	$86.90
7 purchase totals =	$819.46		$900.7100	$900.72	$900.65	$900.80