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	$244.73	11.499%	$272.8715	$272.87	$272.85	$272.90
Purchase #2	$112.56	3.847%	$116.8902	$116.89	$116.90	$116.90
Purchase #3	$230.54	10.411%	$254.5415	$254.54	$254.55	$254.50
Purchase #4	$89.85	9.808%	$98.6625	$98.66	$98.65	$98.70
Purchase #5	$162.39	6.406%	$172.7927	$172.79	$172.80	$172.80
Purchase #6	$88.62	13.409%	$100.5031	$100.50	$100.50	$100.50
Purchase #7	$113.33	11.595%	$126.4706	$126.47	$126.45	$126.50
7 purchase totals =	$1,042.02		$1,142.7321	$1,142.72	$1,142.70	$1,142.80