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	$31.31	9.575%	$34.3079	$34.31	$34.30	$34.30
Purchase #2	$153.27	13.232%	$173.5507	$173.55	$173.55	$173.60
Purchase #3	$104.71	7.358%	$112.4146	$112.41	$112.40	$112.40
Purchase #4	$114.53	7.643%	$123.2835	$123.28	$123.30	$123.30
Purchase #5	$10.29	10.267%	$11.3465	$11.35	$11.35	$11.30
Purchase #6	$169.91	12.458%	$191.0774	$191.08	$191.10	$191.10
Purchase #7	$110.37	3.707%	$114.4614	$114.46	$114.45	$114.50
7 purchase totals =	$694.39		$760.4420	$760.44	$760.45	$760.50