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	$44.96	3.203%	$46.4001	$46.40	$46.40	$46.40
Purchase #2	$204.34	11.663%	$228.1722	$228.17	$228.15	$228.20
Purchase #3	$81.83	8.735%	$88.9779	$88.98	$89.00	$89.00
Purchase #4	$99.74	11.866%	$111.5751	$111.58	$111.60	$111.60
Purchase #5	$205.35	4.356%	$214.295	$214.30	$214.30	$214.30
Purchase #6	$39.89	7.693%	$42.9587	$42.96	$42.95	$43.00
Purchase #7	$105.89	3.734%	$109.8439	$109.84	$109.85	$109.80
7 purchase totals =	$782.00		$842.2229	$842.23	$842.25	$842.30