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	$245.48	7.792%	$264.6078	$264.61	$264.60	$264.60
Purchase #2	$42.54	4.733%	$44.5534	$44.55	$44.55	$44.60
Purchase #3	$214.93	12.335%	$241.4416	$241.44	$241.45	$241.40
Purchase #4	$92.91	11.496%	$103.5909	$103.59	$103.60	$103.60
Purchase #5	$17.83	12.693%	$20.0932	$20.09	$20.10	$20.10
Purchase #6	$110.77	8.278%	$119.9395	$119.94	$119.95	$119.90
Purchase #7	$49.96	12.109%	$56.0097	$56.01	$56.00	$56.00
7 purchase totals =	$774.42		$850.2361	$850.23	$850.25	$850.20