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	$60.30	7.278%	$64.6886	$64.69	$64.70	$64.70
Purchase #2	$122.51	4.147%	$127.5905	$127.59	$127.60	$127.60
Purchase #3	$157.62	6.732%	$168.231	$168.23	$168.25	$168.20
Purchase #4	$217.47	11.243%	$241.9202	$241.92	$241.90	$241.90
Purchase #5	$21.44	9.177%	$23.4075	$23.41	$23.40	$23.40
Purchase #6	$50.73	7.684%	$54.6281	$54.63	$54.65	$54.60
Purchase #7	$30.52	4.520%	$31.8995	$31.90	$31.90	$31.90
7 purchase totals =	$660.59		$712.3654	$712.37	$712.40	$712.30