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	$39.77	7.226%	$42.6438	$42.64	$42.65	$42.60
Purchase #2	$148.28	11.176%	$164.8518	$164.85	$164.85	$164.90
Purchase #3	$139.73	5.308%	$147.1469	$147.15	$147.15	$147.10
Purchase #4	$147.92	3.823%	$153.575	$153.58	$153.60	$153.60
Purchase #5	$135.88	10.617%	$150.3064	$150.31	$150.30	$150.30
Purchase #6	$119.69	6.643%	$127.641	$127.64	$127.65	$127.60
Purchase #7	$187.36	11.767%	$209.4067	$209.41	$209.40	$209.40
7 purchase totals =	$918.63		$995.5716	$995.58	$995.60	$995.50