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	$37.44	7.697%	$40.3218	$40.32	$40.30	$40.30
Purchase #2	$105.49	5.526%	$111.3194	$111.32	$111.30	$111.30
Purchase #3	$108.64	13.869%	$123.7073	$123.71	$123.70	$123.70
Purchase #4	$250.63	7.426%	$269.2418	$269.24	$269.25	$269.20
Purchase #5	$27.99	5.193%	$29.4435	$29.44	$29.45	$29.40
Purchase #6	$241.71	12.606%	$272.18	$272.18	$272.20	$272.20
Purchase #7	$156.69	11.223%	$174.2753	$174.28	$174.30	$174.30
7 purchase totals =	$928.59		$1,020.4891	$1,020.49	$1,020.50	$1,020.40