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	$100.53	11.208%	$111.7974	$111.80	$111.80	$111.80
Purchase #2	$231.67	3.436%	$239.6302	$239.63	$239.65	$239.60
Purchase #3	$6.42	6.182%	$6.8169	$6.82	$6.80	$6.80
Purchase #4	$118.76	11.242%	$132.111	$132.11	$132.10	$132.10
Purchase #5	$128.44	4.248%	$133.8961	$133.90	$133.90	$133.90
Purchase #6	$90.56	9.232%	$98.9205	$98.92	$98.90	$98.90
Purchase #7	$93.93	6.868%	$100.3811	$100.38	$100.40	$100.40
7 purchase totals =	$770.31		$823.5532	$823.56	$823.55	$823.50