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	$153.53	7.552%	$165.1246	$165.12	$165.10	$165.10
Purchase #2	$239.94	11.769%	$268.1785	$268.18	$268.20	$268.20
Purchase #3	$106.89	12.325%	$120.0642	$120.06	$120.05	$120.10
Purchase #4	$148.82	5.366%	$156.8057	$156.81	$156.80	$156.80
Purchase #5	$129.89	11.752%	$145.1547	$145.15	$145.15	$145.20
Purchase #6	$121.81	8.263%	$131.8752	$131.88	$131.90	$131.90
Purchase #7	$39.60	4.826%	$41.5111	$41.51	$41.50	$41.50
7 purchase totals =	$940.48		$1,028.7140	$1,028.71	$1,028.70	$1,028.80