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	$121.30	12.355%	$136.2866	$136.29	$136.30	$136.30
Purchase #2	$128.62	10.864%	$142.5933	$142.59	$142.60	$142.60
Purchase #3	$117.60	8.766%	$127.9088	$127.91	$127.90	$127.90
Purchase #4	$56.65	13.836%	$64.4881	$64.49	$64.50	$64.50
Purchase #5	$94.83	13.385%	$107.523	$107.52	$107.50	$107.50
Purchase #6	$180.57	10.373%	$199.3005	$199.30	$199.30	$199.30
Purchase #7	$113.67	11.232%	$126.4374	$126.44	$126.45	$126.40
7 purchase totals =	$813.24		$904.5377	$904.54	$904.55	$904.50