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	$117.82	11.445%	$131.3045	$131.30	$131.30	$131.30
Purchase #2	$142.56	12.710%	$160.6794	$160.68	$160.70	$160.70
Purchase #3	$105.92	3.132%	$109.2374	$109.24	$109.25	$109.20
Purchase #4	$28.76	10.514%	$31.7838	$31.78	$31.80	$31.80
Purchase #5	$60.46	9.168%	$66.003	$66.00	$66.00	$66.00
Purchase #6	$46.69	3.372%	$48.2644	$48.26	$48.25	$48.30
Purchase #7	$147.86	5.223%	$155.5827	$155.58	$155.60	$155.60
7 purchase totals =	$650.07		$702.8552	$702.84	$702.90	$702.90