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	$175.41	11.834%	$196.168	$196.17	$196.15	$196.20
Purchase #2	$92.70	9.478%	$101.4861	$101.49	$101.50	$101.50
Purchase #3	$105.31	5.699%	$111.3116	$111.31	$111.30	$111.30
Purchase #4	$74.52	5.121%	$78.3362	$78.34	$78.35	$78.30
Purchase #5	$247.72	11.167%	$275.3829	$275.38	$275.40	$275.40
Purchase #6	$60.31	13.218%	$68.2818	$68.28	$68.30	$68.30
Purchase #7	$134.73	3.439%	$139.3634	$139.36	$139.35	$139.40
7 purchase totals =	$890.70		$970.3300	$970.33	$970.35	$970.40