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	$85.84	3.445%	$88.7972	$88.80	$88.80	$88.80
Purchase #2	$52.91	9.287%	$57.8238	$57.82	$57.80	$57.80
Purchase #3	$149.84	6.670%	$159.8343	$159.83	$159.85	$159.80
Purchase #4	$226.58	3.132%	$233.6765	$233.68	$233.70	$233.70
Purchase #5	$80.29	13.206%	$90.8931	$90.89	$90.90	$90.90
Purchase #6	$186.65	12.697%	$210.349	$210.35	$210.35	$210.30
Purchase #7	$89.49	3.491%	$92.6141	$92.61	$92.60	$92.60
7 purchase totals =	$871.60		$933.9880	$933.98	$934.00	$933.90