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	$233.94	8.271%	$253.2892	$253.29	$253.30	$253.30
Purchase #2	$129.83	13.587%	$147.47	$147.47	$147.45	$147.50
Purchase #3	$64.99	4.428%	$67.8678	$67.87	$67.85	$67.90
Purchase #4	$234.86	8.782%	$255.4854	$255.49	$255.50	$255.50
Purchase #5	$53.87	13.233%	$60.9986	$61.00	$61.00	$61.00
Purchase #6	$118.33	7.796%	$127.555	$127.56	$127.55	$127.60
Purchase #7	$6.55	7.136%	$7.0174	$7.02	$7.00	$7.00
7 purchase totals =	$842.37		$919.6834	$919.70	$919.65	$919.80