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	$12.64	7.470%	$13.5842	$13.58	$13.60	$13.60
Purchase #2	$149.36	10.654%	$165.2728	$165.27	$165.25	$165.30
Purchase #3	$85.98	5.323%	$90.5567	$90.56	$90.55	$90.60
Purchase #4	$209.78	6.196%	$222.778	$222.78	$222.80	$222.80
Purchase #5	$135.35	6.103%	$143.6104	$143.61	$143.60	$143.60
Purchase #6	$105.75	7.313%	$113.4835	$113.48	$113.50	$113.50
Purchase #7	$156.48	8.799%	$170.2487	$170.25	$170.25	$170.20
7 purchase totals =	$855.34		$919.5343	$919.53	$919.55	$919.60