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	$49.85	9.519%	$54.5952	$54.60	$54.60	$54.60
Purchase #2	$201.95	5.760%	$213.5823	$213.58	$213.60	$213.60
Purchase #3	$173.30	10.112%	$190.8241	$190.82	$190.80	$190.80
Purchase #4	$233.82	3.129%	$241.1362	$241.14	$241.15	$241.10
Purchase #5	$55.31	6.727%	$59.0307	$59.03	$59.05	$59.00
Purchase #6	$63.96	7.866%	$68.9911	$68.99	$69.00	$69.00
Purchase #7	$144.87	4.535%	$151.4399	$151.44	$151.45	$151.40
7 purchase totals =	$923.06		$979.5995	$979.60	$979.65	$979.50