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	$32.35	13.719%	$36.7881	$36.79	$36.80	$36.80
Purchase #2	$244.48	6.632%	$260.6939	$260.69	$260.70	$260.70
Purchase #3	$123.30	3.752%	$127.9262	$127.93	$127.95	$127.90
Purchase #4	$73.46	11.262%	$81.7331	$81.73	$81.75	$81.70
Purchase #5	$191.55	10.217%	$211.1207	$211.12	$211.10	$211.10
Purchase #6	$242.39	13.288%	$274.5988	$274.60	$274.60	$274.60
Purchase #7	$133.79	9.661%	$146.7155	$146.72	$146.70	$146.70
7 purchase totals =	$1,041.32		$1,139.5763	$1,139.58	$1,139.60	$1,139.50