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	$83.30	9.142%	$90.9153	$90.92	$90.90	$90.90
Purchase #2	$244.43	5.167%	$257.0597	$257.06	$257.05	$257.10
Purchase #3	$190.65	13.775%	$216.912	$216.91	$216.90	$216.90
Purchase #4	$113.61	11.788%	$127.0023	$127.00	$127.00	$127.00
Purchase #5	$127.58	5.710%	$134.8648	$134.86	$134.85	$134.90
Purchase #6	$35.84	12.801%	$40.4279	$40.43	$40.45	$40.40
Purchase #7	$165.69	13.179%	$187.5263	$187.53	$187.55	$187.50
7 purchase totals =	$961.10		$1,054.7083	$1,054.71	$1,054.70	$1,054.70