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	$90.57	10.338%	$99.9331	$99.93	$99.95	$99.90
Purchase #2	$31.54	9.462%	$34.5243	$34.52	$34.50	$34.50
Purchase #3	$208.28	3.461%	$215.4886	$215.49	$215.50	$215.50
Purchase #4	$123.85	4.339%	$129.2239	$129.22	$129.20	$129.20
Purchase #5	$40.48	11.626%	$45.1862	$45.19	$45.20	$45.20
Purchase #6	$54.69	10.508%	$60.4368	$60.44	$60.45	$60.40
Purchase #7	$9.83	8.760%	$10.6911	$10.69	$10.70	$10.70
7 purchase totals =	$559.24		$595.4840	$595.48	$595.50	$595.40