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	$103.48	5.810%	$109.4922	$109.49	$109.50	$109.50
Purchase #2	$54.29	4.656%	$56.8177	$56.82	$56.80	$56.80
Purchase #3	$231.85	13.110%	$262.2455	$262.25	$262.25	$262.20
Purchase #4	$52.34	3.288%	$54.0609	$54.06	$54.05	$54.10
Purchase #5	$25.84	6.634%	$27.5542	$27.55	$27.55	$27.60
Purchase #6	$243.80	12.686%	$274.7285	$274.73	$274.75	$274.70
Purchase #7	$79.75	11.451%	$88.8822	$88.88	$88.90	$88.90
7 purchase totals =	$791.35		$873.7812	$873.78	$873.80	$873.80