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	$33.76	13.214%	$38.221	$38.22	$38.20	$38.20
Purchase #2	$43.48	13.723%	$49.4468	$49.45	$49.45	$49.40
Purchase #3	$26.76	10.394%	$29.5414	$29.54	$29.55	$29.50
Purchase #4	$243.69	9.351%	$266.4775	$266.48	$266.50	$266.50
Purchase #5	$128.61	11.541%	$143.4529	$143.45	$143.45	$143.50
Purchase #6	$79.50	11.388%	$88.5535	$88.55	$88.55	$88.60
Purchase #7	$59.76	4.521%	$62.4617	$62.46	$62.45	$62.50
7 purchase totals =	$615.56		$678.1548	$678.15	$678.15	$678.20