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	$28.30	7.663%	$30.4686	$30.47	$30.45	$30.50
Purchase #2	$172.36	9.179%	$188.1809	$188.18	$188.20	$188.20
Purchase #3	$34.26	12.707%	$38.6134	$38.61	$38.60	$38.60
Purchase #4	$155.27	12.596%	$174.8278	$174.83	$174.85	$174.80
Purchase #5	$165.55	4.331%	$172.72	$172.72	$172.70	$172.70
Purchase #6	$159.53	10.608%	$176.4529	$176.45	$176.45	$176.50
Purchase #7	$19.45	5.534%	$20.5264	$20.53	$20.55	$20.50
7 purchase totals =	$734.72		$801.7900	$801.79	$801.80	$801.80