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	$243.25	4.653%	$254.5684	$254.57	$254.55	$254.60
Purchase #2	$38.63	9.248%	$42.2025	$42.20	$42.20	$42.20
Purchase #3	$222.64	3.808%	$231.1181	$231.12	$231.10	$231.10
Purchase #4	$31.85	7.615%	$34.2754	$34.28	$34.30	$34.30
Purchase #5	$153.84	4.408%	$160.6213	$160.62	$160.60	$160.60
Purchase #6	$124.39	12.221%	$139.5917	$139.59	$139.60	$139.60
Purchase #7	$105.95	9.850%	$116.3861	$116.39	$116.40	$116.40
7 purchase totals =	$920.55		$978.7635	$978.77	$978.75	$978.80