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	$34.75	6.827%	$37.1224	$37.12	$37.10	$37.10
Purchase #2	$94.56	13.365%	$107.1979	$107.20	$107.20	$107.20
Purchase #3	$46.98	12.640%	$52.9183	$52.92	$52.90	$52.90
Purchase #4	$73.66	5.209%	$77.4969	$77.50	$77.50	$77.50
Purchase #5	$155.51	10.705%	$172.1573	$172.16	$172.15	$172.20
Purchase #6	$30.29	7.616%	$32.5969	$32.60	$32.60	$32.60
Purchase #7	$100.94	7.845%	$108.8587	$108.86	$108.85	$108.90
7 purchase totals =	$536.69		$588.3484	$588.36	$588.30	$588.40