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	$51.48	13.442%	$58.3999	$58.40	$58.40	$58.40
Purchase #2	$232.78	7.261%	$249.6822	$249.68	$249.70	$249.70
Purchase #3	$227.94	12.205%	$255.7601	$255.76	$255.75	$255.80
Purchase #4	$138.65	4.475%	$144.8546	$144.85	$144.85	$144.90
Purchase #5	$19.68	8.177%	$21.2892	$21.29	$21.30	$21.30
Purchase #6	$68.27	7.615%	$73.4688	$73.47	$73.45	$73.50
Purchase #7	$99.71	11.650%	$111.3262	$111.33	$111.35	$111.30
7 purchase totals =	$838.51		$914.7810	$914.78	$914.80	$914.90