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	$233.73	12.612%	$263.208	$263.21	$263.20	$263.20
Purchase #2	$146.60	3.739%	$152.0814	$152.08	$152.10	$152.10
Purchase #3	$242.90	3.198%	$250.6679	$250.67	$250.65	$250.70
Purchase #4	$146.40	12.233%	$164.3091	$164.31	$164.30	$164.30
Purchase #5	$107.84	3.494%	$111.6079	$111.61	$111.60	$111.60
Purchase #6	$51.44	9.269%	$56.208	$56.21	$56.20	$56.20
Purchase #7	$78.44	9.278%	$85.7177	$85.72	$85.70	$85.70
7 purchase totals =	$1,007.35		$1,083.8000	$1,083.81	$1,083.75	$1,083.80