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	$160.99	6.370%	$171.2451	$171.25	$171.25	$171.20
Purchase #2	$112.83	12.723%	$127.1854	$127.19	$127.20	$127.20
Purchase #3	$64.44	13.139%	$72.9068	$72.91	$72.90	$72.90
Purchase #4	$152.52	9.803%	$167.4715	$167.47	$167.45	$167.50
Purchase #5	$6.67	8.553%	$7.2405	$7.24	$7.25	$7.20
Purchase #6	$137.90	5.139%	$144.9867	$144.99	$145.00	$145.00
Purchase #7	$141.86	3.355%	$146.6194	$146.62	$146.60	$146.60
7 purchase totals =	$777.21		$837.6554	$837.67	$837.65	$837.60