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	$134.86	5.335%	$142.0548	$142.05	$142.05	$142.10
Purchase #2	$106.32	3.723%	$110.2783	$110.28	$110.30	$110.30
Purchase #3	$78.78	9.225%	$86.0475	$86.05	$86.05	$86.00
Purchase #4	$105.91	9.828%	$116.3188	$116.32	$116.30	$116.30
Purchase #5	$88.70	12.538%	$99.8212	$99.82	$99.80	$99.80
Purchase #6	$20.55	6.340%	$21.8529	$21.85	$21.85	$21.90
Purchase #7	$203.59	10.596%	$225.1624	$225.16	$225.15	$225.20
7 purchase totals =	$738.71		$801.5359	$801.53	$801.50	$801.60