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	$166.73	10.187%	$183.7148	$183.71	$183.70	$183.70
Purchase #2	$24.72	4.645%	$25.8682	$25.87	$25.85	$25.90
Purchase #3	$143.39	13.547%	$162.815	$162.82	$162.80	$162.80
Purchase #4	$75.26	6.514%	$80.1624	$80.16	$80.15	$80.20
Purchase #5	$185.65	12.112%	$208.1359	$208.14	$208.15	$208.10
Purchase #6	$46.92	5.480%	$49.4912	$49.49	$49.50	$49.50
Purchase #7	$83.90	7.381%	$90.0927	$90.09	$90.10	$90.10
7 purchase totals =	$726.57		$800.2802	$800.28	$800.25	$800.30