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	$244.55	10.253%	$269.6237	$269.62	$269.60	$269.60
Purchase #2	$185.59	5.781%	$196.319	$196.32	$196.30	$196.30
Purchase #3	$92.83	9.385%	$101.5421	$101.54	$101.55	$101.50
Purchase #4	$211.27	4.748%	$221.3011	$221.30	$221.30	$221.30
Purchase #5	$24.97	10.550%	$27.6043	$27.60	$27.60	$27.60
Purchase #6	$37.57	13.611%	$42.6837	$42.68	$42.70	$42.70
Purchase #7	$115.37	10.328%	$127.2854	$127.29	$127.30	$127.30
7 purchase totals =	$912.15		$986.3593	$986.35	$986.35	$986.30