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	$147.91	11.660%	$165.1563	$165.16	$165.15	$165.20
Purchase #2	$79.81	3.310%	$82.4517	$82.45	$82.45	$82.50
Purchase #3	$115.74	3.827%	$120.1694	$120.17	$120.15	$120.20
Purchase #4	$118.49	13.613%	$134.62	$134.62	$134.60	$134.60
Purchase #5	$154.74	9.783%	$169.8782	$169.88	$169.90	$169.90
Purchase #6	$206.39	5.297%	$217.3225	$217.32	$217.30	$217.30
Purchase #7	$80.86	10.438%	$89.3002	$89.30	$89.30	$89.30
7 purchase totals =	$903.94		$978.8983	$978.90	$978.85	$979.00