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	$17.33	3.837%	$17.995	$18.00	$18.00	$18.00
Purchase #2	$82.30	12.431%	$92.5307	$92.53	$92.55	$92.50
Purchase #3	$239.43	11.341%	$266.5838	$266.58	$266.60	$266.60
Purchase #4	$140.39	3.685%	$145.5634	$145.56	$145.55	$145.60
Purchase #5	$34.63	4.740%	$36.2715	$36.27	$36.25	$36.30
Purchase #6	$172.38	7.665%	$185.5929	$185.59	$185.60	$185.60
Purchase #7	$222.46	3.786%	$230.8823	$230.88	$230.90	$230.90
7 purchase totals =	$908.92		$975.4196	$975.41	$975.45	$975.50