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	$72.86	10.640%	$80.6123	$80.61	$80.60	$80.60
Purchase #2	$51.91	11.527%	$57.8937	$57.89	$57.90	$57.90
Purchase #3	$145.79	11.748%	$162.9174	$162.92	$162.90	$162.90
Purchase #4	$70.92	10.651%	$78.4737	$78.47	$78.45	$78.50
Purchase #5	$89.75	4.321%	$93.6281	$93.63	$93.65	$93.60
Purchase #6	$98.62	5.804%	$104.3439	$104.34	$104.35	$104.30
Purchase #7	$126.25	10.786%	$139.8673	$139.87	$139.85	$139.90
7 purchase totals =	$656.10		$717.7364	$717.73	$717.70	$717.70