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	$41.29	10.129%	$45.4723	$45.47	$45.45	$45.50
Purchase #2	$21.59	13.335%	$24.469	$24.47	$24.45	$24.50
Purchase #3	$125.63	6.701%	$134.0485	$134.05	$134.05	$134.00
Purchase #4	$235.83	8.521%	$255.9251	$255.93	$255.95	$255.90
Purchase #5	$21.79	13.552%	$24.743	$24.74	$24.75	$24.70
Purchase #6	$188.84	10.572%	$208.8042	$208.80	$208.80	$208.80
Purchase #7	$81.28	10.550%	$89.855	$89.86	$89.85	$89.90
7 purchase totals =	$716.25		$783.3171	$783.32	$783.30	$783.30