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	$52.41	5.829%	$55.465	$55.47	$55.45	$55.50
Purchase #2	$86.37	3.392%	$89.2997	$89.30	$89.30	$89.30
Purchase #3	$151.41	13.785%	$172.2819	$172.28	$172.30	$172.30
Purchase #4	$52.79	3.396%	$54.5827	$54.58	$54.60	$54.60
Purchase #5	$96.79	12.146%	$108.5461	$108.55	$108.55	$108.50
Purchase #6	$216.63	6.389%	$230.4705	$230.47	$230.45	$230.50
Purchase #7	$126.62	6.593%	$134.9681	$134.97	$134.95	$135.00
7 purchase totals =	$783.02		$845.6140	$845.62	$845.60	$845.70