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	$25.70	4.206%	$26.7809	$26.78	$26.80	$26.80
Purchase #2	$178.45	6.170%	$189.4604	$189.46	$189.45	$189.50
Purchase #3	$52.99	11.360%	$59.0097	$59.01	$59.00	$59.00
Purchase #4	$214.36	7.585%	$230.6192	$230.62	$230.60	$230.60
Purchase #5	$183.82	9.260%	$200.8417	$200.84	$200.85	$200.80
Purchase #6	$65.79	8.569%	$71.4275	$71.43	$71.45	$71.40
Purchase #7	$215.60	11.461%	$240.3099	$240.31	$240.30	$240.30
7 purchase totals =	$936.71		$1,018.4493	$1,018.45	$1,018.45	$1,018.40