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	$85.54	5.401%	$90.16	$90.16	$90.15	$90.20
Purchase #2	$193.99	8.663%	$210.7954	$210.80	$210.80	$210.80
Purchase #3	$220.42	11.437%	$245.6294	$245.63	$245.65	$245.60
Purchase #4	$172.59	7.131%	$184.8974	$184.90	$184.90	$184.90
Purchase #5	$114.41	3.188%	$118.0574	$118.06	$118.05	$118.10
Purchase #6	$11.82	4.354%	$12.3346	$12.33	$12.35	$12.30
Purchase #7	$33.94	13.843%	$38.6383	$38.64	$38.65	$38.60
7 purchase totals =	$832.71		$900.5125	$900.52	$900.55	$900.50