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	$145.38	8.819%	$158.2011	$158.20	$158.20	$158.20
Purchase #2	$244.25	10.323%	$269.4639	$269.46	$269.45	$269.50
Purchase #3	$163.79	5.137%	$172.2039	$172.20	$172.20	$172.20
Purchase #4	$99.30	5.359%	$104.6215	$104.62	$104.60	$104.60
Purchase #5	$69.63	5.421%	$73.4046	$73.40	$73.40	$73.40
Purchase #6	$25.60	4.358%	$26.7156	$26.72	$26.70	$26.70
Purchase #7	$82.50	8.812%	$89.7699	$89.77	$89.75	$89.80
7 purchase totals =	$830.45		$894.3805	$894.37	$894.30	$894.40