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	$117.56	12.129%	$131.8189	$131.82	$131.80	$131.80
Purchase #2	$166.39	10.728%	$184.2403	$184.24	$184.25	$184.20
Purchase #3	$207.58	5.638%	$219.2834	$219.28	$219.30	$219.30
Purchase #4	$210.28	5.401%	$221.6372	$221.64	$221.65	$221.60
Purchase #5	$6.86	5.357%	$7.2275	$7.23	$7.25	$7.20
Purchase #6	$157.34	11.754%	$175.8337	$175.83	$175.85	$175.80
Purchase #7	$35.39	8.385%	$38.3575	$38.36	$38.35	$38.40
7 purchase totals =	$901.40		$978.3985	$978.40	$978.45	$978.30