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	$207.28	5.158%	$217.9715	$217.97	$217.95	$218.00
Purchase #2	$200.62	9.795%	$220.2707	$220.27	$220.25	$220.30
Purchase #3	$52.25	3.589%	$54.1253	$54.13	$54.15	$54.10
Purchase #4	$246.67	7.393%	$264.9063	$264.91	$264.90	$264.90
Purchase #5	$18.51	13.340%	$20.9792	$20.98	$21.00	$21.00
Purchase #6	$81.96	10.232%	$90.3461	$90.35	$90.35	$90.30
Purchase #7	$102.31	7.767%	$110.2564	$110.26	$110.25	$110.30
7 purchase totals =	$909.60		$978.8555	$978.87	$978.85	$978.90