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	$74.85	5.403%	$78.8941	$78.89	$78.90	$78.90
Purchase #2	$158.95	10.658%	$175.8909	$175.89	$175.90	$175.90
Purchase #3	$54.27	11.538%	$60.5317	$60.53	$60.55	$60.50
Purchase #4	$29.91	8.336%	$32.4033	$32.40	$32.40	$32.40
Purchase #5	$57.34	9.282%	$62.6623	$62.66	$62.65	$62.70
Purchase #6	$70.68	13.371%	$80.1306	$80.13	$80.15	$80.10
Purchase #7	$212.38	6.177%	$225.4987	$225.50	$225.50	$225.50
7 purchase totals =	$658.38		$716.0116	$716.00	$716.05	$716.00