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	$40.97	13.242%	$46.3952	$46.40	$46.40	$46.40
Purchase #2	$160.83	12.832%	$181.4677	$181.47	$181.45	$181.50
Purchase #3	$139.71	11.779%	$156.1664	$156.17	$156.15	$156.20
Purchase #4	$130.25	5.206%	$137.0308	$137.03	$137.05	$137.00
Purchase #5	$98.30	8.350%	$106.5081	$106.51	$106.50	$106.50
Purchase #6	$55.99	5.865%	$59.2738	$59.27	$59.25	$59.30
Purchase #7	$157.68	9.255%	$172.2733	$172.27	$172.25	$172.30
7 purchase totals =	$783.73		$859.1153	$859.12	$859.05	$859.20