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	$6.94	11.817%	$7.7601	$7.76	$7.75	$7.80
Purchase #2	$220.85	5.618%	$233.2574	$233.26	$233.25	$233.30
Purchase #3	$229.38	13.656%	$260.7041	$260.70	$260.70	$260.70
Purchase #4	$160.30	13.434%	$181.8347	$181.83	$181.85	$181.80
Purchase #5	$59.33	10.383%	$65.4902	$65.49	$65.50	$65.50
Purchase #6	$231.53	10.278%	$255.3267	$255.33	$255.35	$255.30
Purchase #7	$57.99	7.724%	$62.4691	$62.47	$62.45	$62.50
7 purchase totals =	$966.32		$1,066.8423	$1,066.84	$1,066.85	$1,066.90