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	$88.42	11.648%	$98.7192	$98.72	$98.70	$98.70
Purchase #2	$217.55	5.180%	$228.8191	$228.82	$228.80	$228.80
Purchase #3	$78.51	7.265%	$84.2138	$84.21	$84.20	$84.20
Purchase #4	$143.94	6.646%	$153.5063	$153.51	$153.50	$153.50
Purchase #5	$111.45	11.167%	$123.8956	$123.90	$123.90	$123.90
Purchase #6	$138.63	10.693%	$153.4537	$153.45	$153.45	$153.50
Purchase #7	$250.61	13.767%	$285.1115	$285.11	$285.10	$285.10
7 purchase totals =	$1,029.11		$1,127.7192	$1,127.72	$1,127.65	$1,127.70