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	$82.35	3.427%	$85.1721	$85.17	$85.15	$85.20
Purchase #2	$103.61	3.142%	$106.8654	$106.87	$106.85	$106.90
Purchase #3	$207.86	7.314%	$223.0629	$223.06	$223.05	$223.10
Purchase #4	$10.28	10.119%	$11.3202	$11.32	$11.30	$11.30
Purchase #5	$53.67	11.251%	$59.7084	$59.71	$59.70	$59.70
Purchase #6	$78.86	5.312%	$83.049	$83.05	$83.05	$83.00
Purchase #7	$108.70	11.244%	$120.9222	$120.92	$120.90	$120.90
7 purchase totals =	$645.33		$690.1002	$690.10	$690.00	$690.10