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	$94.83	6.639%	$101.1258	$101.13	$101.15	$101.10
Purchase #2	$242.95	11.356%	$270.5394	$270.54	$270.55	$270.50
Purchase #3	$84.32	7.733%	$90.8405	$90.84	$90.85	$90.80
Purchase #4	$208.84	7.342%	$224.173	$224.17	$224.15	$224.20
Purchase #5	$52.86	7.193%	$56.6622	$56.66	$56.65	$56.70
Purchase #6	$187.47	9.129%	$204.5841	$204.58	$204.60	$204.60
Purchase #7	$48.56	9.624%	$53.2334	$53.23	$53.25	$53.20
7 purchase totals =	$919.83		$1,001.1584	$1,001.15	$1,001.20	$1,001.10