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	$18.66	6.243%	$19.8249	$19.82	$19.80	$19.80
Purchase #2	$177.80	11.308%	$197.9056	$197.91	$197.90	$197.90
Purchase #3	$189.91	3.310%	$196.196	$196.20	$196.20	$196.20
Purchase #4	$12.57	10.271%	$13.8611	$13.86	$13.85	$13.90
Purchase #5	$163.32	5.195%	$171.8045	$171.80	$171.80	$171.80
Purchase #6	$79.80	13.564%	$90.6241	$90.62	$90.60	$90.60
Purchase #7	$42.70	8.280%	$46.2356	$46.24	$46.25	$46.20
7 purchase totals =	$684.76		$736.4518	$736.45	$736.40	$736.40