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	$22.91	7.414%	$24.6085	$24.61	$24.60	$24.60
Purchase #2	$236.57	12.696%	$266.6049	$266.60	$266.60	$266.60
Purchase #3	$93.40	9.729%	$102.4869	$102.49	$102.50	$102.50
Purchase #4	$150.76	7.707%	$162.3791	$162.38	$162.40	$162.40
Purchase #5	$86.70	5.359%	$91.3463	$91.35	$91.35	$91.30
Purchase #6	$99.33	6.637%	$105.9225	$105.92	$105.90	$105.90
Purchase #7	$230.36	10.866%	$255.3909	$255.39	$255.40	$255.40
7 purchase totals =	$920.03		$1,008.7391	$1,008.74	$1,008.75	$1,008.70