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	$7.72	11.168%	$8.5822	$8.58	$8.60	$8.60
Purchase #2	$43.66	3.440%	$45.1619	$45.16	$45.15	$45.20
Purchase #3	$94.93	4.769%	$99.4572	$99.46	$99.45	$99.50
Purchase #4	$61.75	12.485%	$69.4595	$69.46	$69.45	$69.50
Purchase #5	$40.61	6.755%	$43.3532	$43.35	$43.35	$43.40
Purchase #6	$196.25	6.102%	$208.2252	$208.23	$208.25	$208.20
Purchase #7	$196.83	8.130%	$212.8323	$212.83	$212.85	$212.80
7 purchase totals =	$641.75		$687.0715	$687.07	$687.10	$687.20