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	$37.62	6.223%	$39.9611	$39.96	$39.95	$40.00
Purchase #2	$126.85	13.776%	$144.3249	$144.32	$144.30	$144.30
Purchase #3	$179.90	8.279%	$194.7939	$194.79	$194.80	$194.80
Purchase #4	$111.62	5.614%	$117.8863	$117.89	$117.90	$117.90
Purchase #5	$96.84	11.456%	$107.934	$107.93	$107.95	$107.90
Purchase #6	$50.63	4.333%	$52.8238	$52.82	$52.80	$52.80
Purchase #7	$39.47	7.422%	$42.3995	$42.40	$42.40	$42.40
7 purchase totals =	$642.93		$700.1235	$700.11	$700.10	$700.10