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	$86.32	6.794%	$92.1846	$92.18	$92.20	$92.20
Purchase #2	$207.98	10.528%	$229.8761	$229.88	$229.90	$229.90
Purchase #3	$54.62	11.191%	$60.7325	$60.73	$60.75	$60.70
Purchase #4	$47.45	7.459%	$50.9893	$50.99	$51.00	$51.00
Purchase #5	$223.73	6.682%	$238.6796	$238.68	$238.70	$238.70
Purchase #6	$81.81	9.552%	$89.6245	$89.62	$89.60	$89.60
Purchase #7	$52.54	4.245%	$54.7703	$54.77	$54.75	$54.80
7 purchase totals =	$754.45		$816.8569	$816.85	$816.90	$816.90