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	$73.53	7.251%	$78.8617	$78.86	$78.85	$78.90
Purchase #2	$50.57	5.489%	$53.3458	$53.35	$53.35	$53.30
Purchase #3	$9.84	6.404%	$10.4702	$10.47	$10.45	$10.50
Purchase #4	$70.53	11.777%	$78.8363	$78.84	$78.85	$78.80
Purchase #5	$172.31	7.606%	$185.4159	$185.42	$185.40	$185.40
Purchase #6	$37.64	4.314%	$39.2638	$39.26	$39.25	$39.30
Purchase #7	$204.46	6.164%	$217.0629	$217.06	$217.05	$217.10
7 purchase totals =	$618.88		$663.2566	$663.26	$663.20	$663.30