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	$190.89	13.599%	$216.8491	$216.85	$216.85	$216.80
Purchase #2	$148.35	10.293%	$163.6197	$163.62	$163.60	$163.60
Purchase #3	$151.51	4.692%	$158.6188	$158.62	$158.60	$158.60
Purchase #4	$79.95	3.432%	$82.6939	$82.69	$82.70	$82.70
Purchase #5	$72.53	8.294%	$78.5456	$78.55	$78.55	$78.50
Purchase #6	$46.86	9.853%	$51.4771	$51.48	$51.50	$51.50
Purchase #7	$186.74	12.504%	$210.09	$210.09	$210.10	$210.10
7 purchase totals =	$876.83		$961.8942	$961.90	$961.90	$961.80