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	$163.95	9.157%	$178.9629	$178.96	$178.95	$179.00
Purchase #2	$81.40	12.866%	$91.8729	$91.87	$91.85	$91.90
Purchase #3	$227.69	4.797%	$238.6123	$238.61	$238.60	$238.60
Purchase #4	$75.30	13.780%	$85.6763	$85.68	$85.70	$85.70
Purchase #5	$37.56	3.258%	$38.7837	$38.78	$38.80	$38.80
Purchase #6	$35.58	12.592%	$40.0602	$40.06	$40.05	$40.10
Purchase #7	$105.32	8.616%	$114.3944	$114.39	$114.40	$114.40
7 purchase totals =	$726.80		$788.3627	$788.35	$788.35	$788.50