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	$31.31	13.141%	$35.4244	$35.42	$35.40	$35.40
Purchase #2	$160.78	11.648%	$179.5077	$179.51	$179.50	$179.50
Purchase #3	$139.94	10.152%	$154.1467	$154.15	$154.15	$154.10
Purchase #4	$90.69	11.174%	$100.8237	$100.82	$100.80	$100.80
Purchase #5	$43.26	8.403%	$46.8951	$46.90	$46.90	$46.90
Purchase #6	$193.83	11.674%	$216.4577	$216.46	$216.45	$216.50
Purchase #7	$77.26	12.252%	$86.7259	$86.73	$86.75	$86.70
7 purchase totals =	$737.07		$819.9812	$819.99	$819.95	$819.90