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	$249.29	11.151%	$277.0883	$277.09	$277.10	$277.10
Purchase #2	$68.78	13.836%	$78.2964	$78.30	$78.30	$78.30
Purchase #3	$71.94	11.406%	$80.1455	$80.15	$80.15	$80.10
Purchase #4	$17.61	4.163%	$18.3431	$18.34	$18.35	$18.30
Purchase #5	$91.28	13.163%	$103.2952	$103.30	$103.30	$103.30
Purchase #6	$151.28	3.566%	$156.6746	$156.67	$156.65	$156.70
Purchase #7	$114.93	11.518%	$128.1676	$128.17	$128.15	$128.20
7 purchase totals =	$765.11		$842.0107	$842.02	$842.00	$842.00