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	$235.90	4.839%	$247.3152	$247.32	$247.30	$247.30
Purchase #2	$235.82	10.637%	$260.9042	$260.90	$260.90	$260.90
Purchase #3	$41.42	4.668%	$43.3535	$43.35	$43.35	$43.40
Purchase #4	$91.45	10.247%	$100.8209	$100.82	$100.80	$100.80
Purchase #5	$11.67	7.605%	$12.5575	$12.56	$12.55	$12.60
Purchase #6	$19.35	3.594%	$20.0454	$20.05	$20.05	$20.00
Purchase #7	$92.96	3.185%	$95.9208	$95.92	$95.90	$95.90
7 purchase totals =	$728.57		$780.9175	$780.92	$780.85	$780.90