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	$50.38	5.849%	$53.3267	$53.33	$53.35	$53.30
Purchase #2	$148.49	10.111%	$163.5038	$163.50	$163.50	$163.50
Purchase #3	$133.44	5.567%	$140.8686	$140.87	$140.85	$140.90
Purchase #4	$157.51	13.372%	$178.5722	$178.57	$178.55	$178.60
Purchase #5	$83.63	7.716%	$90.0829	$90.08	$90.10	$90.10
Purchase #6	$222.86	5.820%	$235.8305	$235.83	$235.85	$235.80
Purchase #7	$127.72	12.523%	$143.7144	$143.71	$143.70	$143.70
7 purchase totals =	$924.03		$1,005.8991	$1,005.89	$1,005.90	$1,005.90