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	$187.58	4.607%	$196.2218	$196.22	$196.20	$196.20
Purchase #2	$40.57	12.585%	$45.6757	$45.68	$45.70	$45.70
Purchase #3	$112.44	13.503%	$127.6228	$127.62	$127.60	$127.60
Purchase #4	$49.47	12.122%	$55.4668	$55.47	$55.45	$55.50
Purchase #5	$217.46	11.569%	$242.6179	$242.62	$242.60	$242.60
Purchase #6	$90.34	13.342%	$102.3932	$102.39	$102.40	$102.40
Purchase #7	$48.62	5.717%	$51.3996	$51.40	$51.40	$51.40
7 purchase totals =	$746.48		$821.3978	$821.40	$821.35	$821.40