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	$28.94	9.285%	$31.6271	$31.63	$31.65	$31.60
Purchase #2	$170.97	11.739%	$191.0402	$191.04	$191.05	$191.00
Purchase #3	$66.88	5.395%	$70.4882	$70.49	$70.50	$70.50
Purchase #4	$152.51	8.231%	$165.0631	$165.06	$165.05	$165.10
Purchase #5	$154.60	7.652%	$166.43	$166.43	$166.45	$166.40
Purchase #6	$17.35	9.344%	$18.9712	$18.97	$18.95	$19.00
Purchase #7	$146.52	4.366%	$152.9171	$152.92	$152.90	$152.90
7 purchase totals =	$737.77		$796.5369	$796.54	$796.55	$796.50