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	$79.32	5.703%	$83.8436	$83.84	$83.85	$83.80
Purchase #2	$124.91	5.436%	$131.7001	$131.70	$131.70	$131.70
Purchase #3	$100.82	11.669%	$112.5847	$112.58	$112.60	$112.60
Purchase #4	$78.43	12.433%	$88.1812	$88.18	$88.20	$88.20
Purchase #5	$166.82	12.528%	$187.7192	$187.72	$187.70	$187.70
Purchase #6	$231.78	8.478%	$251.4303	$251.43	$251.45	$251.40
Purchase #7	$71.48	6.844%	$76.3721	$76.37	$76.35	$76.40
7 purchase totals =	$853.56		$931.8312	$931.82	$931.85	$931.80