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	$120.48	13.615%	$136.8834	$136.88	$136.90	$136.90
Purchase #2	$143.94	10.122%	$158.5096	$158.51	$158.50	$158.50
Purchase #3	$20.93	4.602%	$21.8932	$21.89	$21.90	$21.90
Purchase #4	$149.85	7.542%	$161.1517	$161.15	$161.15	$161.20
Purchase #5	$244.83	4.352%	$255.485	$255.49	$255.50	$255.50
Purchase #6	$35.68	4.459%	$37.271	$37.27	$37.25	$37.30
Purchase #7	$63.56	10.165%	$70.0209	$70.02	$70.00	$70.00
7 purchase totals =	$779.27		$841.2148	$841.21	$841.20	$841.30