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	$207.79	13.169%	$235.1539	$235.15	$235.15	$235.20
Purchase #2	$61.28	9.485%	$67.0924	$67.09	$67.10	$67.10
Purchase #3	$88.46	4.553%	$92.4876	$92.49	$92.50	$92.50
Purchase #4	$160.89	4.253%	$167.7327	$167.73	$167.75	$167.70
Purchase #5	$21.86	9.305%	$23.8941	$23.89	$23.90	$23.90
Purchase #6	$118.45	11.178%	$131.6903	$131.69	$131.70	$131.70
Purchase #7	$231.73	4.637%	$242.4753	$242.48	$242.50	$242.50
7 purchase totals =	$890.46		$960.5263	$960.52	$960.60	$960.60