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	$19.34	7.456%	$20.782	$20.78	$20.80	$20.80
Purchase #2	$56.77	4.605%	$59.3843	$59.38	$59.40	$59.40
Purchase #3	$31.67	3.131%	$32.6616	$32.66	$32.65	$32.70
Purchase #4	$64.86	6.763%	$69.2465	$69.25	$69.25	$69.20
Purchase #5	$17.34	11.388%	$19.3147	$19.31	$19.30	$19.30
Purchase #6	$189.71	9.134%	$207.0381	$207.04	$207.05	$207.00
Purchase #7	$155.71	8.288%	$168.6152	$168.62	$168.60	$168.60
7 purchase totals =	$535.40		$577.0424	$577.04	$577.05	$577.00