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	$182.35	9.582%	$199.8228	$199.82	$199.80	$199.80
Purchase #2	$62.79	4.267%	$65.4692	$65.47	$65.45	$65.50
Purchase #3	$84.52	9.841%	$92.8376	$92.84	$92.85	$92.80
Purchase #4	$45.68	12.692%	$51.4777	$51.48	$51.50	$51.50
Purchase #5	$37.79	10.294%	$41.6801	$41.68	$41.70	$41.70
Purchase #6	$96.66	13.680%	$109.8831	$109.88	$109.90	$109.90
Purchase #7	$19.46	4.267%	$20.2904	$20.29	$20.30	$20.30
7 purchase totals =	$529.25		$581.4609	$581.46	$581.50	$581.50