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	$9.81	11.375%	$10.9259	$10.93	$10.95	$10.90
Purchase #2	$115.56	4.562%	$120.8318	$120.83	$120.85	$120.80
Purchase #3	$101.51	4.111%	$105.6831	$105.68	$105.70	$105.70
Purchase #4	$219.54	13.727%	$249.6763	$249.68	$249.70	$249.70
Purchase #5	$220.39	9.838%	$242.072	$242.07	$242.05	$242.10
Purchase #6	$197.93	5.795%	$209.4	$209.40	$209.40	$209.40
Purchase #7	$107.81	3.823%	$111.9316	$111.93	$111.95	$111.90
7 purchase totals =	$972.55		$1,050.5207	$1,050.52	$1,050.60	$1,050.50