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	$82.67	13.742%	$94.0305	$94.03	$94.05	$94.00
Purchase #2	$145.46	7.780%	$156.7768	$156.78	$156.80	$156.80
Purchase #3	$126.90	9.532%	$138.9961	$139.00	$139.00	$139.00
Purchase #4	$73.25	11.761%	$81.8649	$81.86	$81.85	$81.90
Purchase #5	$154.88	11.453%	$172.6184	$172.62	$172.60	$172.60
Purchase #6	$90.83	6.860%	$97.0609	$97.06	$97.05	$97.10
Purchase #7	$241.31	9.599%	$264.4733	$264.47	$264.45	$264.50
7 purchase totals =	$915.30		$1,005.8209	$1,005.82	$1,005.80	$1,005.90