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	$19.38	4.453%	$20.243	$20.24	$20.25	$20.20
Purchase #2	$98.84	13.302%	$111.9877	$111.99	$112.00	$112.00
Purchase #3	$218.94	10.362%	$241.6266	$241.63	$241.65	$241.60
Purchase #4	$97.27	12.420%	$109.3509	$109.35	$109.35	$109.40
Purchase #5	$116.81	9.317%	$127.6932	$127.69	$127.70	$127.70
Purchase #6	$197.87	10.308%	$218.2664	$218.27	$218.25	$218.30
Purchase #7	$29.95	11.250%	$33.3194	$33.32	$33.30	$33.30
7 purchase totals =	$779.06		$862.4872	$862.49	$862.50	$862.50