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	$78.56	8.170%	$84.9784	$84.98	$85.00	$85.00
Purchase #2	$39.98	12.385%	$44.9315	$44.93	$44.95	$44.90
Purchase #3	$202.57	7.486%	$217.7344	$217.73	$217.75	$217.70
Purchase #4	$48.82	3.615%	$50.5848	$50.58	$50.60	$50.60
Purchase #5	$12.79	13.845%	$14.5608	$14.56	$14.55	$14.60
Purchase #6	$33.56	5.672%	$35.4635	$35.46	$35.45	$35.50
Purchase #7	$209.62	4.501%	$219.055	$219.06	$219.05	$219.10
7 purchase totals =	$625.90		$667.3084	$667.30	$667.35	$667.40