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	$242.94	3.530%	$251.5158	$251.52	$251.50	$251.50
Purchase #2	$65.40	4.158%	$68.1193	$68.12	$68.10	$68.10
Purchase #3	$173.31	8.650%	$188.3013	$188.30	$188.30	$188.30
Purchase #4	$80.79	11.852%	$90.3652	$90.37	$90.35	$90.40
Purchase #5	$154.85	8.564%	$168.1114	$168.11	$168.10	$168.10
Purchase #6	$221.68	5.619%	$234.1362	$234.14	$234.15	$234.10
Purchase #7	$47.78	5.217%	$50.2727	$50.27	$50.25	$50.30
7 purchase totals =	$986.75		$1,050.8219	$1,050.83	$1,050.75	$1,050.80