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	$167.74	13.698%	$190.717	$190.72	$190.70	$190.70
Purchase #2	$139.40	8.581%	$151.3619	$151.36	$151.35	$151.40
Purchase #3	$22.56	11.833%	$25.2295	$25.23	$25.25	$25.20
Purchase #4	$68.48	13.840%	$77.9576	$77.96	$77.95	$78.00
Purchase #5	$229.76	6.266%	$244.1568	$244.16	$244.15	$244.20
Purchase #6	$100.38	5.103%	$105.5024	$105.50	$105.50	$105.50
Purchase #7	$190.70	3.231%	$196.8615	$196.86	$196.85	$196.90
7 purchase totals =	$919.02		$991.7867	$991.79	$991.75	$991.90