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	$79.56	13.844%	$90.5743	$90.57	$90.55	$90.60
Purchase #2	$50.85	10.613%	$56.2467	$56.25	$56.25	$56.20
Purchase #3	$24.82	12.322%	$27.8783	$27.88	$27.90	$27.90
Purchase #4	$129.44	9.583%	$141.8442	$141.84	$141.85	$141.80
Purchase #5	$161.43	6.281%	$171.5694	$171.57	$171.55	$171.60
Purchase #6	$247.52	3.454%	$256.0693	$256.07	$256.05	$256.10
Purchase #7	$140.85	12.453%	$158.3901	$158.39	$158.40	$158.40
7 purchase totals =	$834.47		$902.5723	$902.57	$902.55	$902.60