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	$247.86	4.746%	$259.6234	$259.62	$259.60	$259.60
Purchase #2	$150.96	10.227%	$166.3987	$166.40	$166.40	$166.40
Purchase #3	$197.25	6.500%	$210.0713	$210.07	$210.05	$210.10
Purchase #4	$93.56	8.863%	$101.8522	$101.85	$101.85	$101.90
Purchase #5	$164.85	4.663%	$172.537	$172.54	$172.55	$172.50
Purchase #6	$233.25	7.403%	$250.5175	$250.52	$250.50	$250.50
Purchase #7	$176.66	7.719%	$190.2964	$190.30	$190.30	$190.30
7 purchase totals =	$1,264.39		$1,351.2965	$1,351.30	$1,351.25	$1,351.30