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	$101.46	6.583%	$108.1391	$108.14	$108.15	$108.10
Purchase #2	$169.48	8.627%	$184.101	$184.10	$184.10	$184.10
Purchase #3	$91.31	13.626%	$103.7519	$103.75	$103.75	$103.80
Purchase #4	$124.74	11.510%	$139.0976	$139.10	$139.10	$139.10
Purchase #5	$166.53	3.225%	$171.9006	$171.90	$171.90	$171.90
Purchase #6	$210.52	5.344%	$221.7702	$221.77	$221.75	$221.80
Purchase #7	$38.87	9.585%	$42.5957	$42.60	$42.60	$42.60
7 purchase totals =	$902.91		$971.3561	$971.36	$971.35	$971.40