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	$153.52	12.179%	$172.2172	$172.22	$172.20	$172.20
Purchase #2	$244.82	5.507%	$258.3022	$258.30	$258.30	$258.30
Purchase #3	$10.76	12.679%	$12.1243	$12.12	$12.10	$12.10
Purchase #4	$148.83	12.404%	$167.2909	$167.29	$167.30	$167.30
Purchase #5	$99.26	4.194%	$103.423	$103.42	$103.40	$103.40
Purchase #6	$181.32	4.424%	$189.3416	$189.34	$189.35	$189.30
Purchase #7	$7.96	6.220%	$8.4551	$8.46	$8.45	$8.50
7 purchase totals =	$846.47		$911.1543	$911.15	$911.10	$911.10