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	$138.68	5.559%	$146.3892	$146.39	$146.40	$146.40
Purchase #2	$73.32	10.846%	$81.2723	$81.27	$81.25	$81.30
Purchase #3	$170.52	11.865%	$190.7522	$190.75	$190.75	$190.80
Purchase #4	$71.50	10.167%	$78.7694	$78.77	$78.75	$78.80
Purchase #5	$195.47	9.599%	$214.2332	$214.23	$214.25	$214.20
Purchase #6	$221.38	3.819%	$229.8345	$229.83	$229.85	$229.80
Purchase #7	$131.87	11.342%	$146.8267	$146.83	$146.85	$146.80
7 purchase totals =	$1,002.74		$1,088.0775	$1,088.07	$1,088.10	$1,088.10