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	$103.76	3.791%	$107.6935	$107.69	$107.70	$107.70
Purchase #2	$152.56	6.433%	$162.3742	$162.37	$162.35	$162.40
Purchase #3	$73.45	11.856%	$82.1582	$82.16	$82.15	$82.20
Purchase #4	$42.86	5.347%	$45.1517	$45.15	$45.15	$45.20
Purchase #5	$108.80	11.424%	$121.2293	$121.23	$121.25	$121.20
Purchase #6	$217.48	7.571%	$233.9454	$233.95	$233.95	$233.90
Purchase #7	$90.26	4.195%	$94.0464	$94.05	$94.05	$94.00
7 purchase totals =	$789.17		$846.5987	$846.60	$846.60	$846.60