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	$93.82	12.465%	$105.5147	$105.51	$105.50	$105.50
Purchase #2	$242.28	8.397%	$262.6243	$262.62	$262.60	$262.60
Purchase #3	$35.86	11.660%	$40.0413	$40.04	$40.05	$40.00
Purchase #4	$38.46	5.497%	$40.5741	$40.57	$40.55	$40.60
Purchase #5	$204.66	7.638%	$220.2919	$220.29	$220.30	$220.30
Purchase #6	$85.79	5.168%	$90.2236	$90.22	$90.20	$90.20
Purchase #7	$209.85	11.430%	$233.8359	$233.84	$233.85	$233.80
7 purchase totals =	$910.72		$993.1058	$993.09	$993.05	$993.00