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	$91.96	8.176%	$99.4786	$99.48	$99.50	$99.50
Purchase #2	$222.50	8.136%	$240.6026	$240.60	$240.60	$240.60
Purchase #3	$162.29	7.577%	$174.5867	$174.59	$174.60	$174.60
Purchase #4	$109.82	9.147%	$119.8652	$119.87	$119.85	$119.90
Purchase #5	$162.61	5.611%	$171.734	$171.73	$171.75	$171.70
Purchase #6	$54.36	11.326%	$60.5168	$60.52	$60.50	$60.50
Purchase #7	$56.82	8.613%	$61.7139	$61.71	$61.70	$61.70
7 purchase totals =	$860.36		$928.4978	$928.50	$928.50	$928.50