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	$99.93	11.494%	$111.416	$111.42	$111.40	$111.40
Purchase #2	$95.39	11.138%	$106.0145	$106.01	$106.00	$106.00
Purchase #3	$182.36	4.495%	$190.5571	$190.56	$190.55	$190.60
Purchase #4	$93.31	7.117%	$99.9509	$99.95	$99.95	$100.00
Purchase #5	$137.60	13.599%	$156.3122	$156.31	$156.30	$156.30
Purchase #6	$24.25	4.104%	$25.2452	$25.25	$25.25	$25.20
Purchase #7	$111.97	10.199%	$123.3898	$123.39	$123.40	$123.40
7 purchase totals =	$744.81		$812.8857	$812.89	$812.85	$812.90