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	$127.78	12.654%	$143.9493	$143.95	$143.95	$143.90
Purchase #2	$171.42	12.777%	$193.3223	$193.32	$193.30	$193.30
Purchase #3	$150.67	9.591%	$165.1208	$165.12	$165.10	$165.10
Purchase #4	$97.28	5.382%	$102.5156	$102.52	$102.50	$102.50
Purchase #5	$141.42	8.390%	$153.2851	$153.29	$153.30	$153.30
Purchase #6	$80.61	12.401%	$90.6064	$90.61	$90.60	$90.60
Purchase #7	$100.41	12.400%	$112.8608	$112.86	$112.85	$112.90
7 purchase totals =	$869.59		$961.6603	$961.67	$961.60	$961.60