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	$56.82	6.126%	$60.3008	$60.30	$60.30	$60.30
Purchase #2	$210.43	5.574%	$222.1594	$222.16	$222.15	$222.20
Purchase #3	$48.58	11.497%	$54.1652	$54.17	$54.15	$54.20
Purchase #4	$104.44	11.216%	$116.154	$116.15	$116.15	$116.20
Purchase #5	$125.45	13.827%	$142.796	$142.80	$142.80	$142.80
Purchase #6	$100.65	6.173%	$106.8631	$106.86	$106.85	$106.90
Purchase #7	$133.64	5.654%	$141.196	$141.20	$141.20	$141.20
7 purchase totals =	$780.01		$843.6345	$843.64	$843.60	$843.80