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	$119.94	6.455%	$127.6821	$127.68	$127.70	$127.70
Purchase #2	$140.82	12.508%	$158.4338	$158.43	$158.45	$158.40
Purchase #3	$65.43	9.759%	$71.8153	$71.82	$71.80	$71.80
Purchase #4	$65.62	9.667%	$71.9635	$71.96	$71.95	$72.00
Purchase #5	$231.39	10.576%	$255.8618	$255.86	$255.85	$255.90
Purchase #6	$35.97	9.239%	$39.2933	$39.29	$39.30	$39.30
Purchase #7	$110.89	13.159%	$125.482	$125.48	$125.50	$125.50
7 purchase totals =	$770.06		$850.5318	$850.52	$850.55	$850.60