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	$112.80	6.558%	$120.1974	$120.20	$120.20	$120.20
Purchase #2	$146.45	8.354%	$158.6844	$158.68	$158.70	$158.70
Purchase #3	$100.38	11.514%	$111.9378	$111.94	$111.95	$111.90
Purchase #4	$223.60	7.718%	$240.8574	$240.86	$240.85	$240.90
Purchase #5	$51.59	9.653%	$56.57	$56.57	$56.55	$56.60
Purchase #6	$27.32	7.272%	$29.3067	$29.31	$29.30	$29.30
Purchase #7	$196.65	10.688%	$217.668	$217.67	$217.65	$217.70
7 purchase totals =	$858.79		$935.2217	$935.23	$935.20	$935.30