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	$89.60	7.805%	$96.5933	$96.59	$96.60	$96.60
Purchase #2	$46.72	4.513%	$48.8285	$48.83	$48.85	$48.80
Purchase #3	$212.78	9.535%	$233.0686	$233.07	$233.05	$233.10
Purchase #4	$151.89	6.670%	$162.0211	$162.02	$162.00	$162.00
Purchase #5	$32.41	3.811%	$33.6451	$33.65	$33.65	$33.60
Purchase #6	$70.89	12.315%	$79.6201	$79.62	$79.60	$79.60
Purchase #7	$125.28	7.149%	$134.2363	$134.24	$134.25	$134.20
7 purchase totals =	$729.57		$788.0130	$788.02	$788.00	$787.90