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	$67.73	10.801%	$75.0455	$75.05	$75.05	$75.00
Purchase #2	$46.90	7.204%	$50.2787	$50.28	$50.30	$50.30
Purchase #3	$74.64	4.836%	$78.2496	$78.25	$78.25	$78.20
Purchase #4	$147.29	10.351%	$162.536	$162.54	$162.55	$162.50
Purchase #5	$156.30	10.308%	$172.4114	$172.41	$172.40	$172.40
Purchase #6	$76.66	8.605%	$83.2566	$83.26	$83.25	$83.30
Purchase #7	$13.88	12.664%	$15.6378	$15.64	$15.65	$15.60
7 purchase totals =	$583.40		$637.4156	$637.43	$637.45	$637.30