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	$20.33	6.292%	$21.6092	$21.61	$21.60	$21.60
Purchase #2	$131.35	11.539%	$146.5065	$146.51	$146.50	$146.50
Purchase #3	$30.99	9.662%	$33.9843	$33.98	$34.00	$34.00
Purchase #4	$59.25	3.448%	$61.2929	$61.29	$61.30	$61.30
Purchase #5	$102.75	12.821%	$115.9236	$115.92	$115.90	$115.90
Purchase #6	$87.57	7.631%	$94.2525	$94.25	$94.25	$94.30
Purchase #7	$101.26	10.755%	$112.1505	$112.15	$112.15	$112.20
7 purchase totals =	$533.50		$585.7195	$585.71	$585.70	$585.80