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	$42.78	8.646%	$46.4788	$46.48	$46.50	$46.50
Purchase #2	$94.32	5.364%	$99.3793	$99.38	$99.40	$99.40
Purchase #3	$45.93	3.618%	$47.5917	$47.59	$47.60	$47.60
Purchase #4	$183.50	7.842%	$197.8901	$197.89	$197.90	$197.90
Purchase #5	$40.80	4.255%	$42.536	$42.54	$42.55	$42.50
Purchase #6	$119.52	7.828%	$128.876	$128.88	$128.90	$128.90
Purchase #7	$102.75	8.341%	$111.3204	$111.32	$111.30	$111.30
7 purchase totals =	$629.60		$674.0723	$674.08	$674.15	$674.10