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	$129.29	8.193%	$139.8827	$139.88	$139.90	$139.90
Purchase #2	$126.45	4.594%	$132.2591	$132.26	$132.25	$132.30
Purchase #3	$178.85	12.182%	$200.6375	$200.64	$200.65	$200.60
Purchase #4	$178.64	3.679%	$185.2122	$185.21	$185.20	$185.20
Purchase #5	$204.89	12.223%	$229.9337	$229.93	$229.95	$229.90
Purchase #6	$83.92	5.377%	$88.4324	$88.43	$88.45	$88.40
Purchase #7	$188.65	11.694%	$210.7107	$210.71	$210.70	$210.70
7 purchase totals =	$1,090.69		$1,187.0683	$1,187.06	$1,187.10	$1,187.00