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	$142.77	10.769%	$158.1449	$158.14	$158.15	$158.10
Purchase #2	$23.63	6.643%	$25.1997	$25.20	$25.20	$25.20
Purchase #3	$233.54	3.848%	$242.5266	$242.53	$242.55	$242.50
Purchase #4	$28.60	13.527%	$32.4687	$32.47	$32.45	$32.50
Purchase #5	$35.88	5.785%	$37.9557	$37.96	$37.95	$38.00
Purchase #6	$172.86	9.107%	$188.6024	$188.60	$188.60	$188.60
Purchase #7	$47.56	4.274%	$49.5927	$49.59	$49.60	$49.60
7 purchase totals =	$684.84		$734.4907	$734.49	$734.50	$734.50