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	$26.57	11.350%	$29.5857	$29.59	$29.60	$29.60
Purchase #2	$64.71	4.820%	$67.829	$67.83	$67.85	$67.80
Purchase #3	$244.58	13.855%	$278.4666	$278.47	$278.45	$278.50
Purchase #4	$116.89	9.795%	$128.3394	$128.34	$128.35	$128.30
Purchase #5	$142.53	6.564%	$151.8857	$151.89	$151.90	$151.90
Purchase #6	$90.47	10.490%	$99.9603	$99.96	$99.95	$100.00
Purchase #7	$137.78	4.793%	$144.3838	$144.38	$144.40	$144.40
7 purchase totals =	$823.53		$900.4505	$900.46	$900.50	$900.50