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	$150.98	13.252%	$170.9879	$170.99	$171.00	$171.00
Purchase #2	$54.29	5.839%	$57.46	$57.46	$57.45	$57.50
Purchase #3	$150.94	5.193%	$158.7783	$158.78	$158.80	$158.80
Purchase #4	$167.63	3.505%	$173.5054	$173.51	$173.50	$173.50
Purchase #5	$70.91	10.491%	$78.3492	$78.35	$78.35	$78.30
Purchase #6	$211.67	5.534%	$223.3838	$223.38	$223.40	$223.40
Purchase #7	$22.66	11.601%	$25.2888	$25.29	$25.30	$25.30
7 purchase totals =	$829.08		$887.7534	$887.76	$887.80	$887.80