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	$148.96	3.729%	$154.5147	$154.51	$154.50	$154.50
Purchase #2	$223.75	11.855%	$250.2756	$250.28	$250.30	$250.30
Purchase #3	$142.55	11.179%	$158.4857	$158.49	$158.50	$158.50
Purchase #4	$7.61	4.314%	$7.9383	$7.94	$7.95	$7.90
Purchase #5	$152.35	9.211%	$166.383	$166.38	$166.40	$166.40
Purchase #6	$151.86	6.207%	$161.286	$161.29	$161.30	$161.30
Purchase #7	$29.32	5.803%	$31.0214	$31.02	$31.00	$31.00
7 purchase totals =	$856.40		$929.9047	$929.91	$929.95	$929.90