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	$178.32	5.407%	$187.9618	$187.96	$187.95	$188.00
Purchase #2	$141.32	7.326%	$151.6731	$151.67	$151.65	$151.70
Purchase #3	$32.60	9.252%	$35.6162	$35.62	$35.60	$35.60
Purchase #4	$58.36	12.867%	$65.8692	$65.87	$65.85	$65.90
Purchase #5	$97.57	12.511%	$109.777	$109.78	$109.80	$109.80
Purchase #6	$91.37	8.777%	$99.3895	$99.39	$99.40	$99.40
Purchase #7	$15.68	11.798%	$17.5299	$17.53	$17.55	$17.50
7 purchase totals =	$615.22		$667.8167	$667.82	$667.80	$667.90