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	$83.25	8.720%	$90.5094	$90.51	$90.50	$90.50
Purchase #2	$9.98	9.450%	$10.9231	$10.92	$10.90	$10.90
Purchase #3	$34.67	9.123%	$37.8329	$37.83	$37.85	$37.80
Purchase #4	$98.59	4.655%	$103.1794	$103.18	$103.20	$103.20
Purchase #5	$110.90	6.141%	$117.7104	$117.71	$117.70	$117.70
Purchase #6	$166.39	10.288%	$183.5082	$183.51	$183.50	$183.50
Purchase #7	$47.84	10.136%	$52.6891	$52.69	$52.70	$52.70
7 purchase totals =	$551.62		$596.3525	$596.35	$596.35	$596.30