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	$86.81	6.531%	$92.4796	$92.48	$92.50	$92.50
Purchase #2	$177.61	10.839%	$196.8611	$196.86	$196.85	$196.90
Purchase #3	$142.81	11.725%	$159.5545	$159.55	$159.55	$159.60
Purchase #4	$34.44	3.720%	$35.7212	$35.72	$35.70	$35.70
Purchase #5	$248.66	8.626%	$270.1094	$270.11	$270.10	$270.10
Purchase #6	$180.52	5.447%	$190.3529	$190.35	$190.35	$190.40
Purchase #7	$151.65	12.623%	$170.7928	$170.79	$170.80	$170.80
7 purchase totals =	$1,022.50		$1,115.8715	$1,115.86	$1,115.85	$1,116.00