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	$168.77	3.206%	$174.1808	$174.18	$174.20	$174.20
Purchase #2	$133.32	9.554%	$146.0574	$146.06	$146.05	$146.10
Purchase #3	$96.62	6.772%	$103.1631	$103.16	$103.15	$103.20
Purchase #4	$111.70	10.152%	$123.0398	$123.04	$123.05	$123.00
Purchase #5	$95.65	7.125%	$102.4651	$102.47	$102.45	$102.50
Purchase #6	$215.74	3.161%	$222.5595	$222.56	$222.55	$222.60
Purchase #7	$19.59	7.323%	$21.0246	$21.02	$21.00	$21.00
7 purchase totals =	$841.39		$892.4903	$892.49	$892.45	$892.60