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	$231.49	7.794%	$249.5323	$249.53	$249.55	$249.50
Purchase #2	$87.89	13.583%	$99.8281	$99.83	$99.85	$99.80
Purchase #3	$145.26	5.754%	$153.6183	$153.62	$153.60	$153.60
Purchase #4	$21.82	12.758%	$24.6038	$24.60	$24.60	$24.60
Purchase #5	$82.40	11.589%	$91.9493	$91.95	$91.95	$91.90
Purchase #6	$179.39	8.466%	$194.5772	$194.58	$194.60	$194.60
Purchase #7	$31.50	12.736%	$35.5118	$35.51	$35.50	$35.50
7 purchase totals =	$779.75		$849.6208	$849.62	$849.65	$849.50