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	$195.87	12.572%	$220.4948	$220.49	$220.50	$220.50
Purchase #2	$30.50	8.492%	$33.0901	$33.09	$33.10	$33.10
Purchase #3	$142.82	11.397%	$159.0972	$159.10	$159.10	$159.10
Purchase #4	$74.60	7.256%	$80.013	$80.01	$80.00	$80.00
Purchase #5	$21.30	8.507%	$23.112	$23.11	$23.10	$23.10
Purchase #6	$86.78	11.108%	$96.4195	$96.42	$96.40	$96.40
Purchase #7	$38.55	10.683%	$42.6683	$42.67	$42.65	$42.70
7 purchase totals =	$590.42		$654.8949	$654.89	$654.85	$654.90