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	$196.79	10.689%	$217.8249	$217.82	$217.80	$217.80
Purchase #2	$31.43	6.335%	$33.4211	$33.42	$33.40	$33.40
Purchase #3	$6.35	11.322%	$7.0689	$7.07	$7.05	$7.10
Purchase #4	$242.93	13.253%	$275.1255	$275.13	$275.15	$275.10
Purchase #5	$145.37	7.584%	$156.3949	$156.39	$156.40	$156.40
Purchase #6	$211.30	7.819%	$227.8215	$227.82	$227.80	$227.80
Purchase #7	$66.42	11.183%	$73.8477	$73.85	$73.85	$73.80
7 purchase totals =	$900.59		$991.5045	$991.50	$991.45	$991.40