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	$230.98	3.350%	$238.7178	$238.72	$238.70	$238.70
Purchase #2	$38.64	8.872%	$42.0681	$42.07	$42.05	$42.10
Purchase #3	$172.27	6.481%	$183.4348	$183.43	$183.45	$183.40
Purchase #4	$211.91	11.233%	$235.7139	$235.71	$235.70	$235.70
Purchase #5	$111.32	11.284%	$123.8813	$123.88	$123.90	$123.90
Purchase #6	$231.96	10.261%	$255.7614	$255.76	$255.75	$255.80
Purchase #7	$67.25	5.735%	$71.1068	$71.11	$71.10	$71.10
7 purchase totals =	$1,064.33		$1,150.6841	$1,150.68	$1,150.65	$1,150.70