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	$26.64	5.431%	$28.0868	$28.09	$28.10	$28.10
Purchase #2	$155.47	10.740%	$172.1675	$172.17	$172.15	$172.20
Purchase #3	$90.67	5.618%	$95.7638	$95.76	$95.75	$95.80
Purchase #4	$146.32	7.106%	$156.7175	$156.72	$156.70	$156.70
Purchase #5	$200.96	9.104%	$219.2554	$219.26	$219.25	$219.30
Purchase #6	$31.40	3.178%	$32.3979	$32.40	$32.40	$32.40
Purchase #7	$117.93	11.290%	$131.2443	$131.24	$131.25	$131.20
7 purchase totals =	$769.39		$835.6332	$835.64	$835.60	$835.70