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	$149.40	12.498%	$168.072	$168.07	$168.05	$168.10
Purchase #2	$223.90	5.337%	$235.8495	$235.85	$235.85	$235.80
Purchase #3	$88.57	13.848%	$100.8352	$100.84	$100.85	$100.80
Purchase #4	$164.32	4.776%	$172.1679	$172.17	$172.15	$172.20
Purchase #5	$38.91	12.310%	$43.6998	$43.70	$43.70	$43.70
Purchase #6	$118.87	6.843%	$127.0043	$127.00	$127.00	$127.00
Purchase #7	$6.57	3.537%	$6.8024	$6.80	$6.80	$6.80
7 purchase totals =	$790.54		$854.4311	$854.43	$854.40	$854.40