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	$76.44	12.870%	$86.2778	$86.28	$86.30	$86.30
Purchase #2	$143.38	5.599%	$151.4078	$151.41	$151.40	$151.40
Purchase #3	$187.85	6.377%	$199.8292	$199.83	$199.85	$199.80
Purchase #4	$191.60	11.467%	$213.5708	$213.57	$213.55	$213.60
Purchase #5	$46.46	13.715%	$52.832	$52.83	$52.85	$52.80
Purchase #6	$28.79	8.245%	$31.1637	$31.16	$31.15	$31.20
Purchase #7	$139.32	4.174%	$145.1352	$145.14	$145.15	$145.10
7 purchase totals =	$813.84		$880.2165	$880.22	$880.25	$880.20