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	$69.60	13.104%	$78.7204	$78.72	$78.70	$78.70
Purchase #2	$151.43	4.586%	$158.3746	$158.37	$158.35	$158.40
Purchase #3	$168.53	6.788%	$179.9698	$179.97	$179.95	$180.00
Purchase #4	$125.67	11.329%	$139.9072	$139.91	$139.90	$139.90
Purchase #5	$223.27	9.573%	$244.6436	$244.64	$244.65	$244.60
Purchase #6	$181.39	13.833%	$206.4817	$206.48	$206.50	$206.50
Purchase #7	$99.98	13.542%	$113.5193	$113.52	$113.50	$113.50
7 purchase totals =	$1,019.87		$1,121.6166	$1,121.61	$1,121.55	$1,121.60