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	$39.39	5.314%	$41.4832	$41.48	$41.50	$41.50
Purchase #2	$233.40	13.665%	$265.2941	$265.29	$265.30	$265.30
Purchase #3	$189.99	10.596%	$210.1213	$210.12	$210.10	$210.10
Purchase #4	$180.42	3.763%	$187.2092	$187.21	$187.20	$187.20
Purchase #5	$33.45	13.786%	$38.0614	$38.06	$38.05	$38.10
Purchase #6	$176.91	12.211%	$198.5125	$198.51	$198.50	$198.50
Purchase #7	$229.60	13.279%	$260.0886	$260.09	$260.10	$260.10
7 purchase totals =	$1,083.16		$1,200.7703	$1,200.76	$1,200.75	$1,200.80