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	$204.98	5.850%	$216.9713	$216.97	$216.95	$217.00
Purchase #2	$45.48	6.216%	$48.307	$48.31	$48.30	$48.30
Purchase #3	$54.38	12.694%	$61.283	$61.28	$61.30	$61.30
Purchase #4	$242.39	13.603%	$275.3623	$275.36	$275.35	$275.40
Purchase #5	$214.69	6.154%	$227.902	$227.90	$227.90	$227.90
Purchase #6	$14.47	6.393%	$15.3951	$15.40	$15.40	$15.40
Purchase #7	$117.85	12.701%	$132.8181	$132.82	$132.80	$132.80
7 purchase totals =	$894.24		$978.0388	$978.04	$978.00	$978.10