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	$96.30	4.446%	$100.5815	$100.58	$100.60	$100.60
Purchase #2	$53.47	7.522%	$57.492	$57.49	$57.50	$57.50
Purchase #3	$56.69	10.280%	$62.5177	$62.52	$62.50	$62.50
Purchase #4	$41.42	7.628%	$44.5795	$44.58	$44.60	$44.60
Purchase #5	$244.72	8.370%	$265.2031	$265.20	$265.20	$265.20
Purchase #6	$56.55	6.866%	$60.4327	$60.43	$60.45	$60.40
Purchase #7	$29.46	11.649%	$32.8918	$32.89	$32.90	$32.90
7 purchase totals =	$578.61		$623.6983	$623.69	$623.75	$623.70