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	$31.91	5.669%	$33.719	$33.72	$33.70	$33.70
Purchase #2	$244.30	11.445%	$272.2601	$272.26	$272.25	$272.30
Purchase #3	$38.59	4.413%	$40.293	$40.29	$40.30	$40.30
Purchase #4	$167.44	3.306%	$172.9756	$172.98	$173.00	$173.00
Purchase #5	$127.27	8.438%	$138.009	$138.01	$138.00	$138.00
Purchase #6	$230.63	4.172%	$240.2519	$240.25	$240.25	$240.30
Purchase #7	$37.91	12.348%	$42.5911	$42.59	$42.60	$42.60
7 purchase totals =	$878.05		$940.0997	$940.10	$940.10	$940.20