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	$211.57	12.138%	$237.2504	$237.25	$237.25	$237.30
Purchase #2	$161.85	5.290%	$170.4119	$170.41	$170.40	$170.40
Purchase #3	$84.97	5.471%	$89.6187	$89.62	$89.60	$89.60
Purchase #4	$144.89	12.261%	$162.655	$162.66	$162.65	$162.70
Purchase #5	$30.96	5.461%	$32.6507	$32.65	$32.65	$32.70
Purchase #6	$132.66	9.757%	$145.6036	$145.60	$145.60	$145.60
Purchase #7	$63.74	13.451%	$72.3137	$72.31	$72.30	$72.30
7 purchase totals =	$830.64		$910.5040	$910.50	$910.45	$910.60