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	$57.61	7.205%	$61.7608	$61.76	$61.75	$61.80
Purchase #2	$124.91	11.242%	$138.9524	$138.95	$138.95	$139.00
Purchase #3	$248.78	11.491%	$277.3673	$277.37	$277.35	$277.40
Purchase #4	$188.49	11.732%	$210.6036	$210.60	$210.60	$210.60
Purchase #5	$61.52	5.382%	$64.831	$64.83	$64.85	$64.80
Purchase #6	$124.50	12.112%	$139.5794	$139.58	$139.60	$139.60
Purchase #7	$36.91	9.862%	$40.5501	$40.55	$40.55	$40.60
7 purchase totals =	$842.72		$933.6446	$933.64	$933.65	$933.80