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	$80.91	10.221%	$89.1798	$89.18	$89.20	$89.20
Purchase #2	$147.89	10.292%	$163.1108	$163.11	$163.10	$163.10
Purchase #3	$104.44	6.599%	$111.332	$111.33	$111.35	$111.30
Purchase #4	$66.72	6.823%	$71.2723	$71.27	$71.25	$71.30
Purchase #5	$30.39	8.103%	$32.8525	$32.85	$32.85	$32.90
Purchase #6	$51.66	8.548%	$56.0759	$56.08	$56.10	$56.10
Purchase #7	$155.68	3.114%	$160.5279	$160.53	$160.55	$160.50
7 purchase totals =	$637.69		$684.3512	$684.35	$684.40	$684.40