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	$161.83	6.837%	$172.8943	$172.89	$172.90	$172.90
Purchase #2	$31.30	12.141%	$35.1001	$35.10	$35.10	$35.10
Purchase #3	$51.95	6.172%	$55.1564	$55.16	$55.15	$55.20
Purchase #4	$98.51	12.775%	$111.0947	$111.09	$111.10	$111.10
Purchase #5	$43.64	11.272%	$48.5591	$48.56	$48.55	$48.60
Purchase #6	$26.71	11.529%	$29.7894	$29.79	$29.80	$29.80
Purchase #7	$52.64	13.189%	$59.5827	$59.58	$59.60	$59.60
7 purchase totals =	$466.58		$512.1767	$512.17	$512.20	$512.30