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	$89.73	12.593%	$101.0297	$101.03	$101.05	$101.00
Purchase #2	$76.73	9.249%	$83.8268	$83.83	$83.85	$83.80
Purchase #3	$13.73	12.763%	$15.4824	$15.48	$15.50	$15.50
Purchase #4	$34.31	3.387%	$35.4721	$35.47	$35.45	$35.50
Purchase #5	$100.44	12.175%	$112.6686	$112.67	$112.65	$112.70
Purchase #6	$146.92	13.784%	$167.1715	$167.17	$167.15	$167.20
Purchase #7	$71.57	11.469%	$79.7784	$79.78	$79.80	$79.80
7 purchase totals =	$533.43		$595.4295	$595.43	$595.45	$595.50