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	$43.55	6.162%	$46.2336	$46.23	$46.25	$46.20
Purchase #2	$110.33	5.480%	$116.3761	$116.38	$116.40	$116.40
Purchase #3	$81.33	13.748%	$92.5112	$92.51	$92.50	$92.50
Purchase #4	$159.97	5.559%	$168.8627	$168.86	$168.85	$168.90
Purchase #5	$230.37	10.615%	$254.8238	$254.82	$254.80	$254.80
Purchase #6	$200.56	4.490%	$209.5651	$209.57	$209.55	$209.60
Purchase #7	$29.52	5.426%	$31.1218	$31.12	$31.10	$31.10
7 purchase totals =	$855.63		$919.4943	$919.49	$919.45	$919.50