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	$7.58	5.357%	$7.9861	$7.99	$8.00	$8.00
Purchase #2	$69.93	12.321%	$78.5461	$78.55	$78.55	$78.50
Purchase #3	$82.27	4.839%	$86.251	$86.25	$86.25	$86.30
Purchase #4	$143.48	4.340%	$149.707	$149.71	$149.70	$149.70
Purchase #5	$170.75	11.525%	$190.4289	$190.43	$190.45	$190.40
Purchase #6	$52.59	7.714%	$56.6468	$56.65	$56.65	$56.60
Purchase #7	$161.88	6.576%	$172.5252	$172.53	$172.55	$172.50
7 purchase totals =	$688.48		$742.0911	$742.11	$742.15	$742.00