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	$78.69	11.745%	$87.9321	$87.93	$87.95	$87.90
Purchase #2	$82.35	11.325%	$91.6761	$91.68	$91.70	$91.70
Purchase #3	$110.77	12.189%	$124.2718	$124.27	$124.25	$124.30
Purchase #4	$234.38	11.758%	$261.9384	$261.94	$261.95	$261.90
Purchase #5	$229.53	11.156%	$255.1364	$255.14	$255.15	$255.10
Purchase #6	$71.96	9.523%	$78.8128	$78.81	$78.80	$78.80
Purchase #7	$74.48	9.491%	$81.5489	$81.55	$81.55	$81.50
7 purchase totals =	$882.16		$981.3165	$981.32	$981.35	$981.20