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	$105.43	6.171%	$111.9361	$111.94	$111.95	$111.90
Purchase #2	$186.65	13.772%	$212.3554	$212.36	$212.35	$212.40
Purchase #3	$65.26	11.481%	$72.7525	$72.75	$72.75	$72.80
Purchase #4	$227.47	10.443%	$251.2247	$251.22	$251.20	$251.20
Purchase #5	$105.30	8.470%	$114.2189	$114.22	$114.20	$114.20
Purchase #6	$24.74	12.349%	$27.7951	$27.80	$27.80	$27.80
Purchase #7	$29.62	13.158%	$33.5174	$33.52	$33.50	$33.50
7 purchase totals =	$744.47		$823.8001	$823.81	$823.75	$823.80