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	$117.76	10.129%	$129.6879	$129.69	$129.70	$129.70
Purchase #2	$181.28	4.218%	$188.9264	$188.93	$188.95	$188.90
Purchase #3	$81.96	10.748%	$90.7691	$90.77	$90.75	$90.80
Purchase #4	$58.27	11.149%	$64.7665	$64.77	$64.75	$64.80
Purchase #5	$73.26	11.275%	$81.5201	$81.52	$81.50	$81.50
Purchase #6	$56.84	7.566%	$61.1405	$61.14	$61.15	$61.10
Purchase #7	$48.31	10.640%	$53.4502	$53.45	$53.45	$53.50
7 purchase totals =	$617.68		$670.2607	$670.27	$670.25	$670.30