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	$78.45	5.298%	$82.6063	$82.61	$82.60	$82.60
Purchase #2	$227.67	12.550%	$256.2426	$256.24	$256.25	$256.20
Purchase #3	$129.38	10.720%	$143.2495	$143.25	$143.25	$143.20
Purchase #4	$223.36	3.799%	$231.8454	$231.85	$231.85	$231.80
Purchase #5	$81.40	5.314%	$85.7256	$85.73	$85.75	$85.70
Purchase #6	$124.62	10.554%	$137.7724	$137.77	$137.75	$137.80
Purchase #7	$153.57	4.343%	$160.2395	$160.24	$160.25	$160.20
7 purchase totals =	$1,018.45		$1,097.6813	$1,097.69	$1,097.70	$1,097.50