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	$229.52	6.546%	$244.5444	$244.54	$244.55	$244.50
Purchase #2	$114.25	11.758%	$127.6835	$127.68	$127.70	$127.70
Purchase #3	$139.67	13.203%	$158.1106	$158.11	$158.10	$158.10
Purchase #4	$53.85	8.639%	$58.5021	$58.50	$58.50	$58.50
Purchase #5	$28.80	13.588%	$32.7133	$32.71	$32.70	$32.70
Purchase #6	$62.60	9.435%	$68.5063	$68.51	$68.50	$68.50
Purchase #7	$90.96	10.264%	$100.2961	$100.30	$100.30	$100.30
7 purchase totals =	$719.65		$790.3563	$790.35	$790.35	$790.30