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	$89.63	11.716%	$100.1311	$100.13	$100.15	$100.10
Purchase #2	$60.72	10.805%	$67.2808	$67.28	$67.30	$67.30
Purchase #3	$220.38	7.151%	$236.1394	$236.14	$236.15	$236.10
Purchase #4	$161.86	11.526%	$180.516	$180.52	$180.50	$180.50
Purchase #5	$38.66	9.375%	$42.2844	$42.28	$42.30	$42.30
Purchase #6	$124.77	5.345%	$131.439	$131.44	$131.45	$131.40
Purchase #7	$35.34	4.859%	$37.0572	$37.06	$37.05	$37.10
7 purchase totals =	$731.36		$794.8479	$794.85	$794.90	$794.80