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	$138.43	12.863%	$156.2363	$156.24	$156.25	$156.20
Purchase #2	$151.41	6.680%	$161.5242	$161.52	$161.50	$161.50
Purchase #3	$205.56	11.836%	$229.8901	$229.89	$229.90	$229.90
Purchase #4	$242.75	3.537%	$251.3361	$251.34	$251.35	$251.30
Purchase #5	$39.69	4.774%	$41.5848	$41.58	$41.60	$41.60
Purchase #6	$103.88	7.387%	$111.5536	$111.55	$111.55	$111.60
Purchase #7	$93.45	11.413%	$104.1154	$104.12	$104.10	$104.10
7 purchase totals =	$975.17		$1,056.2405	$1,056.24	$1,056.25	$1,056.20