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	$224.29	13.645%	$254.8944	$254.89	$254.90	$254.90
Purchase #2	$64.50	12.615%	$72.6367	$72.64	$72.65	$72.60
Purchase #3	$34.40	9.214%	$37.5696	$37.57	$37.55	$37.60
Purchase #4	$49.34	13.322%	$55.9131	$55.91	$55.90	$55.90
Purchase #5	$20.56	11.244%	$22.8718	$22.87	$22.85	$22.90
Purchase #6	$54.32	12.436%	$61.0752	$61.08	$61.10	$61.10
Purchase #7	$227.37	5.424%	$239.7025	$239.70	$239.70	$239.70
7 purchase totals =	$674.78		$744.6633	$744.66	$744.65	$744.70