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	$58.33	13.417%	$66.1561	$66.16	$66.15	$66.20
Purchase #2	$172.63	13.825%	$196.4961	$196.50	$196.50	$196.50
Purchase #3	$205.83	10.277%	$226.9831	$226.98	$227.00	$227.00
Purchase #4	$57.79	11.233%	$64.2816	$64.28	$64.30	$64.30
Purchase #5	$92.51	13.350%	$104.8601	$104.86	$104.85	$104.90
Purchase #6	$229.31	4.518%	$239.6702	$239.67	$239.65	$239.70
Purchase #7	$123.25	3.403%	$127.4442	$127.44	$127.45	$127.40
7 purchase totals =	$939.65		$1,025.8914	$1,025.89	$1,025.90	$1,026.00