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	$49.60	11.831%	$55.4682	$55.47	$55.45	$55.50
Purchase #2	$207.87	7.697%	$223.8698	$223.87	$223.85	$223.90
Purchase #3	$125.57	12.773%	$141.6091	$141.61	$141.60	$141.60
Purchase #4	$63.86	5.546%	$67.4017	$67.40	$67.40	$67.40
Purchase #5	$170.39	9.505%	$186.5856	$186.59	$186.60	$186.60
Purchase #6	$70.62	11.434%	$78.6947	$78.69	$78.70	$78.70
Purchase #7	$13.63	9.118%	$14.8728	$14.87	$14.85	$14.90
7 purchase totals =	$701.54		$768.5019	$768.50	$768.45	$768.60