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	$78.63	9.658%	$86.2241	$86.22	$86.20	$86.20
Purchase #2	$151.56	4.478%	$158.3469	$158.35	$158.35	$158.30
Purchase #3	$82.90	3.419%	$85.7344	$85.73	$85.75	$85.70
Purchase #4	$148.58	10.366%	$163.9818	$163.98	$164.00	$164.00
Purchase #5	$35.53	9.404%	$38.8712	$38.87	$38.85	$38.90
Purchase #6	$102.77	13.437%	$116.5792	$116.58	$116.60	$116.60
Purchase #7	$141.55	9.772%	$155.3823	$155.38	$155.40	$155.40
7 purchase totals =	$741.52		$805.1199	$805.11	$805.15	$805.10