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	$164.58	11.246%	$183.0887	$183.09	$183.10	$183.10
Purchase #2	$186.68	10.514%	$206.3075	$206.31	$206.30	$206.30
Purchase #3	$16.63	9.713%	$18.2453	$18.25	$18.25	$18.20
Purchase #4	$123.87	13.456%	$140.5379	$140.54	$140.55	$140.50
Purchase #5	$122.39	13.629%	$139.0705	$139.07	$139.05	$139.10
Purchase #6	$7.37	4.777%	$7.7221	$7.72	$7.70	$7.70
Purchase #7	$119.66	6.578%	$127.5312	$127.53	$127.55	$127.50
7 purchase totals =	$741.18		$822.5032	$822.51	$822.50	$822.40