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	$29.51	12.187%	$33.1064	$33.11	$33.10	$33.10
Purchase #2	$19.67	6.147%	$20.8791	$20.88	$20.90	$20.90
Purchase #3	$246.82	8.831%	$268.6167	$268.62	$268.60	$268.60
Purchase #4	$139.86	4.613%	$146.3117	$146.31	$146.30	$146.30
Purchase #5	$93.65	10.849%	$103.8101	$103.81	$103.80	$103.80
Purchase #6	$117.27	7.570%	$126.1473	$126.15	$126.15	$126.10
Purchase #7	$188.36	6.259%	$200.1495	$200.15	$200.15	$200.10
7 purchase totals =	$835.14		$899.0208	$899.03	$899.00	$898.90