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	$219.89	9.336%	$240.4189	$240.42	$240.40	$240.40
Purchase #2	$79.31	12.461%	$89.1928	$89.19	$89.20	$89.20
Purchase #3	$62.49	6.232%	$66.3844	$66.38	$66.40	$66.40
Purchase #4	$162.73	10.586%	$179.9566	$179.96	$179.95	$180.00
Purchase #5	$239.89	8.287%	$259.7697	$259.77	$259.75	$259.80
Purchase #6	$97.85	5.548%	$103.2787	$103.28	$103.30	$103.30
Purchase #7	$11.71	6.781%	$12.5041	$12.50	$12.50	$12.50
7 purchase totals =	$873.87		$951.5052	$951.50	$951.50	$951.60