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	$106.46	7.295%	$114.2263	$114.23	$114.25	$114.20
Purchase #2	$210.82	10.696%	$233.3693	$233.37	$233.35	$233.40
Purchase #3	$182.88	4.107%	$190.3909	$190.39	$190.40	$190.40
Purchase #4	$29.67	11.728%	$33.1497	$33.15	$33.15	$33.10
Purchase #5	$26.76	6.200%	$28.4191	$28.42	$28.40	$28.40
Purchase #6	$145.34	8.725%	$158.0209	$158.02	$158.00	$158.00
Purchase #7	$18.97	9.506%	$20.7733	$20.77	$20.75	$20.80
7 purchase totals =	$720.90		$778.3495	$778.35	$778.30	$778.30