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	$79.54	13.641%	$90.3901	$90.39	$90.40	$90.40
Purchase #2	$152.92	4.566%	$159.9023	$159.90	$159.90	$159.90
Purchase #3	$60.56	8.323%	$65.6004	$65.60	$65.60	$65.60
Purchase #4	$232.32	11.552%	$259.1576	$259.16	$259.15	$259.20
Purchase #5	$101.63	9.553%	$111.3387	$111.34	$111.35	$111.30
Purchase #6	$85.81	5.718%	$90.7166	$90.72	$90.70	$90.70
Purchase #7	$219.84	6.130%	$233.3162	$233.32	$233.30	$233.30
7 purchase totals =	$932.62		$1,010.4219	$1,010.43	$1,010.40	$1,010.40