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	$19.65	10.475%	$21.7083	$21.71	$21.70	$21.70
Purchase #2	$89.53	3.119%	$92.3224	$92.32	$92.30	$92.30
Purchase #3	$162.95	13.161%	$184.3958	$184.40	$184.40	$184.40
Purchase #4	$173.56	12.572%	$195.38	$195.38	$195.40	$195.40
Purchase #5	$58.34	9.840%	$64.0807	$64.08	$64.10	$64.10
Purchase #6	$175.96	11.739%	$196.6159	$196.62	$196.60	$196.60
Purchase #7	$160.71	13.181%	$181.8932	$181.89	$181.90	$181.90
7 purchase totals =	$840.70		$936.3963	$936.40	$936.40	$936.40