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	$206.31	6.280%	$219.2663	$219.27	$219.25	$219.30
Purchase #2	$139.65	3.681%	$144.7905	$144.79	$144.80	$144.80
Purchase #3	$224.64	5.772%	$237.6062	$237.61	$237.60	$237.60
Purchase #4	$184.72	4.323%	$192.7054	$192.71	$192.70	$192.70
Purchase #5	$43.73	9.582%	$47.9202	$47.92	$47.90	$47.90
Purchase #6	$150.26	4.360%	$156.8113	$156.81	$156.80	$156.80
Purchase #7	$89.74	12.289%	$100.7681	$100.77	$100.75	$100.80
7 purchase totals =	$1,039.05		$1,099.8680	$1,099.88	$1,099.80	$1,099.90