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	$80.88	12.182%	$90.7328	$90.73	$90.75	$90.70
Purchase #2	$114.55	5.542%	$120.8984	$120.90	$120.90	$120.90
Purchase #3	$226.78	5.689%	$239.6815	$239.68	$239.70	$239.70
Purchase #4	$86.29	12.215%	$96.8303	$96.83	$96.85	$96.80
Purchase #5	$73.68	6.433%	$78.4198	$78.42	$78.40	$78.40
Purchase #6	$76.26	5.805%	$80.6869	$80.69	$80.70	$80.70
Purchase #7	$38.81	4.212%	$40.4447	$40.44	$40.45	$40.40
7 purchase totals =	$697.25		$747.6944	$747.69	$747.75	$747.60