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	$21.33	13.180%	$24.1413	$24.14	$24.15	$24.10
Purchase #2	$48.42	4.450%	$50.5747	$50.57	$50.55	$50.60
Purchase #3	$67.92	5.550%	$71.6896	$71.69	$71.70	$71.70
Purchase #4	$197.47	13.742%	$224.6063	$224.61	$224.60	$224.60
Purchase #5	$47.39	9.575%	$51.9276	$51.93	$51.95	$51.90
Purchase #6	$77.55	10.382%	$85.6012	$85.60	$85.60	$85.60
Purchase #7	$131.40	4.501%	$137.3143	$137.31	$137.30	$137.30
7 purchase totals =	$591.48		$645.8550	$645.85	$645.85	$645.80