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	$5.86	5.795%	$6.1996	$6.20	$6.20	$6.20
Purchase #2	$92.97	8.530%	$100.9003	$100.90	$100.90	$100.90
Purchase #3	$157.75	10.557%	$174.4037	$174.40	$174.40	$174.40
Purchase #4	$76.29	3.369%	$78.8602	$78.86	$78.85	$78.90
Purchase #5	$142.52	12.142%	$159.8248	$159.82	$159.80	$159.80
Purchase #6	$64.33	7.693%	$69.2789	$69.28	$69.30	$69.30
Purchase #7	$33.93	13.635%	$38.5564	$38.56	$38.55	$38.60
7 purchase totals =	$573.65		$628.0239	$628.02	$628.00	$628.10