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	$88.67	12.794%	$100.0144	$100.01	$100.00	$100.00
Purchase #2	$89.83	7.762%	$96.8026	$96.80	$96.80	$96.80
Purchase #3	$21.77	4.168%	$22.6774	$22.68	$22.70	$22.70
Purchase #4	$220.46	10.271%	$243.1034	$243.10	$243.10	$243.10
Purchase #5	$241.72	10.137%	$266.2232	$266.22	$266.20	$266.20
Purchase #6	$225.89	11.430%	$251.7092	$251.71	$251.70	$251.70
Purchase #7	$108.27	13.865%	$123.2816	$123.28	$123.30	$123.30
7 purchase totals =	$996.61		$1,103.8118	$1,103.80	$1,103.80	$1,103.80