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	$72.61	8.788%	$78.991	$78.99	$79.00	$79.00
Purchase #2	$21.86	10.146%	$24.0779	$24.08	$24.10	$24.10
Purchase #3	$47.56	12.480%	$53.4955	$53.50	$53.50	$53.50
Purchase #4	$120.27	13.274%	$136.2346	$136.23	$136.25	$136.20
Purchase #5	$178.93	6.271%	$190.1507	$190.15	$190.15	$190.20
Purchase #6	$105.80	10.218%	$116.6106	$116.61	$116.60	$116.60
Purchase #7	$163.53	10.388%	$180.5175	$180.52	$180.50	$180.50
7 purchase totals =	$710.56		$780.0778	$780.08	$780.10	$780.10