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	$119.54	6.305%	$127.077	$127.08	$127.10	$127.10
Purchase #2	$225.85	8.442%	$244.9163	$244.92	$244.90	$244.90
Purchase #3	$54.27	11.223%	$60.3607	$60.36	$60.35	$60.40
Purchase #4	$144.34	9.345%	$157.8286	$157.83	$157.85	$157.80
Purchase #5	$101.77	9.371%	$111.3069	$111.31	$111.30	$111.30
Purchase #6	$190.86	8.159%	$206.4323	$206.43	$206.45	$206.40
Purchase #7	$10.61	13.459%	$12.038	$12.04	$12.05	$12.00
7 purchase totals =	$847.24		$919.9598	$919.97	$920.00	$919.90