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	$238.84	11.844%	$267.1282	$267.13	$267.15	$267.10
Purchase #2	$147.43	12.394%	$165.7025	$165.70	$165.70	$165.70
Purchase #3	$61.71	7.476%	$66.3234	$66.32	$66.30	$66.30
Purchase #4	$143.31	3.596%	$148.4634	$148.46	$148.45	$148.50
Purchase #5	$155.79	12.710%	$175.5909	$175.59	$175.60	$175.60
Purchase #6	$106.54	4.799%	$111.6529	$111.65	$111.65	$111.70
Purchase #7	$52.77	11.773%	$58.9826	$58.98	$59.00	$59.00
7 purchase totals =	$906.39		$993.8439	$993.83	$993.85	$993.90