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	$128.65	12.648%	$144.9217	$144.92	$144.90	$144.90
Purchase #2	$60.42	7.485%	$64.9424	$64.94	$64.95	$64.90
Purchase #3	$104.90	3.351%	$108.4152	$108.42	$108.40	$108.40
Purchase #4	$179.27	5.328%	$188.8215	$188.82	$188.80	$188.80
Purchase #5	$222.38	12.309%	$249.7528	$249.75	$249.75	$249.80
Purchase #6	$170.96	4.152%	$178.0583	$178.06	$178.05	$178.10
Purchase #7	$162.47	4.801%	$170.2702	$170.27	$170.25	$170.30
7 purchase totals =	$1,029.05		$1,105.1821	$1,105.18	$1,105.10	$1,105.20