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	$37.56	8.245%	$40.6568	$40.66	$40.65	$40.70
Purchase #2	$158.49	7.452%	$170.3007	$170.30	$170.30	$170.30
Purchase #3	$158.45	4.728%	$165.9415	$165.94	$165.95	$165.90
Purchase #4	$71.44	12.113%	$80.0935	$80.09	$80.10	$80.10
Purchase #5	$73.54	12.289%	$82.5773	$82.58	$82.60	$82.60
Purchase #6	$115.35	3.307%	$119.1646	$119.16	$119.15	$119.20
Purchase #7	$5.71	13.238%	$6.4659	$6.47	$6.45	$6.50
7 purchase totals =	$620.54		$665.2003	$665.20	$665.20	$665.30