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	$110.38	12.236%	$123.8861	$123.89	$123.90	$123.90
Purchase #2	$238.52	8.171%	$258.0095	$258.01	$258.00	$258.00
Purchase #3	$55.36	12.467%	$62.2617	$62.26	$62.25	$62.30
Purchase #4	$160.76	4.422%	$167.8688	$167.87	$167.85	$167.90
Purchase #5	$64.81	10.244%	$71.4491	$71.45	$71.45	$71.40
Purchase #6	$215.86	3.406%	$223.2122	$223.21	$223.20	$223.20
Purchase #7	$154.60	11.479%	$172.3465	$172.35	$172.35	$172.30
7 purchase totals =	$1,000.29		$1,079.0339	$1,079.04	$1,079.00	$1,079.00