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	$220.39	12.564%	$248.0798	$248.08	$248.10	$248.10
Purchase #2	$90.90	3.388%	$93.9797	$93.98	$94.00	$94.00
Purchase #3	$234.79	4.628%	$245.6561	$245.66	$245.65	$245.70
Purchase #4	$47.59	10.789%	$52.7245	$52.72	$52.70	$52.70
Purchase #5	$201.52	4.286%	$210.1571	$210.16	$210.15	$210.20
Purchase #6	$90.59	10.236%	$99.8628	$99.86	$99.85	$99.90
Purchase #7	$142.59	4.765%	$149.3844	$149.38	$149.40	$149.40
7 purchase totals =	$1,028.37		$1,099.8444	$1,099.84	$1,099.85	$1,100.00