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	$38.74	4.441%	$40.4604	$40.46	$40.45	$40.50
Purchase #2	$173.69	13.320%	$196.8255	$196.83	$196.85	$196.80
Purchase #3	$25.61	11.501%	$28.5554	$28.56	$28.55	$28.60
Purchase #4	$69.72	9.423%	$76.2897	$76.29	$76.30	$76.30
Purchase #5	$91.50	7.610%	$98.4632	$98.46	$98.45	$98.50
Purchase #6	$127.43	5.622%	$134.5941	$134.59	$134.60	$134.60
Purchase #7	$196.30	5.784%	$207.654	$207.65	$207.65	$207.70
7 purchase totals =	$722.99		$782.8423	$782.84	$782.85	$783.00