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	$70.63	8.408%	$76.5686	$76.57	$76.55	$76.60
Purchase #2	$145.98	4.588%	$152.6776	$152.68	$152.70	$152.70
Purchase #3	$80.55	12.682%	$90.7654	$90.77	$90.75	$90.80
Purchase #4	$105.56	5.384%	$111.2434	$111.24	$111.25	$111.20
Purchase #5	$241.85	9.375%	$264.5234	$264.52	$264.50	$264.50
Purchase #6	$41.89	3.445%	$43.3331	$43.33	$43.35	$43.30
Purchase #7	$132.42	9.434%	$144.9125	$144.91	$144.90	$144.90
7 purchase totals =	$818.88		$884.0240	$884.02	$884.00	$884.00