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	$118.95	7.204%	$127.5192	$127.52	$127.50	$127.50
Purchase #2	$100.56	10.507%	$111.1258	$111.13	$111.15	$111.10
Purchase #3	$201.36	11.417%	$224.3493	$224.35	$224.35	$224.30
Purchase #4	$141.83	9.715%	$155.6088	$155.61	$155.60	$155.60
Purchase #5	$151.58	3.291%	$156.5685	$156.57	$156.55	$156.60
Purchase #6	$115.55	4.390%	$120.6226	$120.62	$120.60	$120.60
Purchase #7	$78.79	8.278%	$85.3122	$85.31	$85.30	$85.30
7 purchase totals =	$908.62		$981.1064	$981.11	$981.05	$981.00