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	$27.42	13.517%	$31.1264	$31.13	$31.15	$31.10
Purchase #2	$133.60	9.309%	$146.0368	$146.04	$146.05	$146.00
Purchase #3	$26.60	6.137%	$28.2324	$28.23	$28.25	$28.20
Purchase #4	$171.31	8.397%	$185.6949	$185.69	$185.70	$185.70
Purchase #5	$175.76	8.686%	$191.0265	$191.03	$191.05	$191.00
Purchase #6	$129.41	9.824%	$142.1232	$142.12	$142.10	$142.10
Purchase #7	$172.52	10.287%	$190.2671	$190.27	$190.25	$190.30
7 purchase totals =	$836.62		$914.5073	$914.51	$914.55	$914.40