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	$135.35	11.867%	$151.412	$151.41	$151.40	$151.40
Purchase #2	$30.59	10.752%	$33.879	$33.88	$33.90	$33.90
Purchase #3	$97.43	8.165%	$105.3852	$105.39	$105.40	$105.40
Purchase #4	$31.72	11.123%	$35.2482	$35.25	$35.25	$35.20
Purchase #5	$132.88	9.245%	$145.1648	$145.16	$145.15	$145.20
Purchase #6	$70.65	4.713%	$73.9797	$73.98	$74.00	$74.00
Purchase #7	$9.55	7.727%	$10.2879	$10.29	$10.30	$10.30
7 purchase totals =	$508.17		$555.3568	$555.36	$555.40	$555.40