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	$50.40	13.356%	$57.1314	$57.13	$57.15	$57.10
Purchase #2	$162.47	8.772%	$176.7219	$176.72	$176.70	$176.70
Purchase #3	$228.42	11.861%	$255.5129	$255.51	$255.50	$255.50
Purchase #4	$249.90	6.298%	$265.6387	$265.64	$265.65	$265.60
Purchase #5	$196.93	7.335%	$211.3748	$211.37	$211.35	$211.40
Purchase #6	$125.66	6.406%	$133.7098	$133.71	$133.70	$133.70
Purchase #7	$158.52	6.530%	$168.8714	$168.87	$168.85	$168.90
7 purchase totals =	$1,172.30		$1,268.9609	$1,268.95	$1,268.90	$1,268.90