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	$68.54	6.556%	$73.0335	$73.03	$73.05	$73.00
Purchase #2	$139.54	9.751%	$153.1465	$153.15	$153.15	$153.10
Purchase #3	$133.91	5.629%	$141.4478	$141.45	$141.45	$141.40
Purchase #4	$54.95	13.809%	$62.538	$62.54	$62.55	$62.50
Purchase #5	$17.57	3.698%	$18.2197	$18.22	$18.20	$18.20
Purchase #6	$31.90	7.694%	$34.3544	$34.35	$34.35	$34.40
Purchase #7	$151.35	13.790%	$172.2212	$172.22	$172.20	$172.20
7 purchase totals =	$597.76		$654.9611	$654.96	$654.95	$654.80