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	$120.32	12.544%	$135.4129	$135.41	$135.40	$135.40
Purchase #2	$164.89	4.798%	$172.8014	$172.80	$172.80	$172.80
Purchase #3	$48.63	8.491%	$52.7592	$52.76	$52.75	$52.80
Purchase #4	$100.47	11.251%	$111.7739	$111.77	$111.75	$111.80
Purchase #5	$73.50	12.110%	$82.4009	$82.40	$82.40	$82.40
Purchase #6	$238.44	12.550%	$268.3642	$268.36	$268.35	$268.40
Purchase #7	$11.97	8.167%	$12.9476	$12.95	$12.95	$12.90
7 purchase totals =	$758.22		$836.4601	$836.45	$836.40	$836.50