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	$89.73	10.859%	$99.4738	$99.47	$99.45	$99.50
Purchase #2	$104.26	4.390%	$108.837	$108.84	$108.85	$108.80
Purchase #3	$25.70	11.674%	$28.7002	$28.70	$28.70	$28.70
Purchase #4	$189.84	12.515%	$213.5985	$213.60	$213.60	$213.60
Purchase #5	$114.60	11.456%	$127.7286	$127.73	$127.75	$127.70
Purchase #6	$159.48	4.303%	$166.3424	$166.34	$166.35	$166.30
Purchase #7	$227.30	11.569%	$253.5963	$253.60	$253.60	$253.60
7 purchase totals =	$910.91		$998.2768	$998.28	$998.30	$998.20