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	$69.31	13.719%	$78.8186	$78.82	$78.80	$78.80
Purchase #2	$56.38	9.374%	$61.6651	$61.67	$61.65	$61.70
Purchase #3	$75.98	8.302%	$82.2879	$82.29	$82.30	$82.30
Purchase #4	$156.48	8.861%	$170.3457	$170.35	$170.35	$170.30
Purchase #5	$40.68	6.233%	$43.2156	$43.22	$43.20	$43.20
Purchase #6	$106.60	10.123%	$117.3911	$117.39	$117.40	$117.40
Purchase #7	$165.49	13.329%	$187.5482	$187.55	$187.55	$187.50
7 purchase totals =	$670.92		$741.2722	$741.29	$741.25	$741.20