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	$69.54	10.864%	$77.0948	$77.09	$77.10	$77.10
Purchase #2	$102.76	5.572%	$108.4858	$108.49	$108.50	$108.50
Purchase #3	$58.93	11.687%	$65.8171	$65.82	$65.80	$65.80
Purchase #4	$53.86	3.202%	$55.5846	$55.58	$55.60	$55.60
Purchase #5	$8.40	6.345%	$8.933	$8.93	$8.95	$8.90
Purchase #6	$79.45	12.505%	$89.3852	$89.39	$89.40	$89.40
Purchase #7	$30.65	4.597%	$32.059	$32.06	$32.05	$32.10
7 purchase totals =	$403.59		$437.3595	$437.36	$437.40	$437.40