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	$105.25	12.487%	$118.3926	$118.39	$118.40	$118.40
Purchase #2	$184.68	6.401%	$196.5014	$196.50	$196.50	$196.50
Purchase #3	$173.87	11.781%	$194.3536	$194.35	$194.35	$194.40
Purchase #4	$92.77	8.194%	$100.3716	$100.37	$100.35	$100.40
Purchase #5	$173.90	12.204%	$195.1228	$195.12	$195.10	$195.10
Purchase #6	$151.41	7.596%	$162.9111	$162.91	$162.90	$162.90
Purchase #7	$231.26	9.865%	$254.0738	$254.07	$254.05	$254.10
7 purchase totals =	$1,113.14		$1,221.7269	$1,221.71	$1,221.65	$1,221.80