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	$193.85	5.156%	$203.8449	$203.84	$203.85	$203.80
Purchase #2	$29.93	8.346%	$32.428	$32.43	$32.45	$32.40
Purchase #3	$221.58	12.171%	$248.5485	$248.55	$248.55	$248.50
Purchase #4	$47.39	5.781%	$50.1296	$50.13	$50.15	$50.10
Purchase #5	$95.51	5.334%	$100.6045	$100.60	$100.60	$100.60
Purchase #6	$140.52	9.492%	$153.8582	$153.86	$153.85	$153.90
Purchase #7	$92.28	7.435%	$99.141	$99.14	$99.15	$99.10
7 purchase totals =	$821.06		$888.5547	$888.55	$888.60	$888.40