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	$145.49	7.325%	$156.1471	$156.15	$156.15	$156.10
Purchase #2	$246.96	4.810%	$258.8388	$258.84	$258.85	$258.80
Purchase #3	$144.73	8.169%	$156.553	$156.55	$156.55	$156.60
Purchase #4	$123.63	3.441%	$127.8841	$127.88	$127.90	$127.90
Purchase #5	$36.59	9.358%	$40.0141	$40.01	$40.00	$40.00
Purchase #6	$36.32	6.495%	$38.679	$38.68	$38.70	$38.70
Purchase #7	$232.39	12.578%	$261.62	$261.62	$261.60	$261.60
7 purchase totals =	$966.11		$1,039.7361	$1,039.73	$1,039.75	$1,039.70