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	$73.75	6.714%	$78.7016	$78.70	$78.70	$78.70
Purchase #2	$147.70	10.119%	$162.6458	$162.65	$162.65	$162.60
Purchase #3	$208.99	6.385%	$222.334	$222.33	$222.35	$222.30
Purchase #4	$61.55	11.447%	$68.5956	$68.60	$68.60	$68.60
Purchase #5	$122.45	12.181%	$137.3656	$137.37	$137.35	$137.40
Purchase #6	$49.29	5.236%	$51.8708	$51.87	$51.85	$51.90
Purchase #7	$33.71	6.501%	$35.9015	$35.90	$35.90	$35.90
7 purchase totals =	$697.44		$757.4149	$757.42	$757.40	$757.40