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	$153.77	8.422%	$166.7205	$166.72	$166.70	$166.70
Purchase #2	$202.83	13.333%	$229.8733	$229.87	$229.85	$229.90
Purchase #3	$123.45	6.768%	$131.8051	$131.81	$131.80	$131.80
Purchase #4	$16.45	6.121%	$17.4569	$17.46	$17.45	$17.50
Purchase #5	$46.79	13.581%	$53.1445	$53.14	$53.15	$53.10
Purchase #6	$105.61	8.251%	$114.3239	$114.32	$114.30	$114.30
Purchase #7	$90.69	11.400%	$101.0287	$101.03	$101.05	$101.00
7 purchase totals =	$739.59		$814.3529	$814.35	$814.30	$814.30