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	$54.96	5.382%	$57.9179	$57.92	$57.90	$57.90
Purchase #2	$19.50	6.544%	$20.7761	$20.78	$20.80	$20.80
Purchase #3	$35.46	6.350%	$37.7117	$37.71	$37.70	$37.70
Purchase #4	$154.89	13.846%	$176.3361	$176.34	$176.35	$176.30
Purchase #5	$119.52	12.313%	$134.2365	$134.24	$134.25	$134.20
Purchase #6	$27.29	7.835%	$29.4282	$29.43	$29.45	$29.40
Purchase #7	$128.34	10.491%	$141.8041	$141.80	$141.80	$141.80
7 purchase totals =	$539.96		$598.2106	$598.22	$598.25	$598.10