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	$41.88	3.519%	$43.3538	$43.35	$43.35	$43.40
Purchase #2	$134.78	11.776%	$150.6517	$150.65	$150.65	$150.70
Purchase #3	$244.91	12.106%	$274.5588	$274.56	$274.55	$274.60
Purchase #4	$171.57	8.665%	$186.4365	$186.44	$186.45	$186.40
Purchase #5	$40.26	13.322%	$45.6234	$45.62	$45.60	$45.60
Purchase #6	$239.75	7.825%	$258.5104	$258.51	$258.50	$258.50
Purchase #7	$116.32	9.718%	$127.624	$127.62	$127.60	$127.60
7 purchase totals =	$989.47		$1,086.7586	$1,086.75	$1,086.70	$1,086.80