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	$220.82	12.234%	$247.8351	$247.84	$247.85	$247.80
Purchase #2	$63.30	5.181%	$66.5796	$66.58	$66.60	$66.60
Purchase #3	$52.48	12.467%	$59.0227	$59.02	$59.00	$59.00
Purchase #4	$220.86	4.368%	$230.5072	$230.51	$230.50	$230.50
Purchase #5	$55.95	13.664%	$63.595	$63.60	$63.60	$63.60
Purchase #6	$46.69	3.443%	$48.2975	$48.30	$48.30	$48.30
Purchase #7	$107.80	6.594%	$114.9083	$114.91	$114.90	$114.90
7 purchase totals =	$767.90		$830.7454	$830.76	$830.75	$830.70