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	$85.91	4.605%	$89.8662	$89.87	$89.85	$89.90
Purchase #2	$53.68	13.868%	$61.1243	$61.12	$61.10	$61.10
Purchase #3	$148.39	12.480%	$166.9091	$166.91	$166.90	$166.90
Purchase #4	$143.72	8.855%	$156.4464	$156.45	$156.45	$156.40
Purchase #5	$71.92	11.636%	$80.2886	$80.29	$80.30	$80.30
Purchase #6	$87.73	9.310%	$95.8977	$95.90	$95.90	$95.90
Purchase #7	$161.92	7.267%	$173.6867	$173.69	$173.70	$173.70
7 purchase totals =	$753.27		$824.2190	$824.23	$824.20	$824.20