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	$115.76	9.739%	$127.0339	$127.03	$127.05	$127.00
Purchase #2	$107.30	3.657%	$111.224	$111.22	$111.20	$111.20
Purchase #3	$135.85	4.501%	$141.9646	$141.96	$141.95	$142.00
Purchase #4	$159.61	13.800%	$181.6362	$181.64	$181.65	$181.60
Purchase #5	$69.60	5.315%	$73.2992	$73.30	$73.30	$73.30
Purchase #6	$35.76	10.245%	$39.4236	$39.42	$39.40	$39.40
Purchase #7	$130.56	10.742%	$144.5848	$144.58	$144.60	$144.60
7 purchase totals =	$754.44		$819.1663	$819.15	$819.15	$819.10