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	$52.56	8.652%	$57.1075	$57.11	$57.10	$57.10
Purchase #2	$37.25	4.846%	$39.0551	$39.06	$39.05	$39.10
Purchase #3	$34.84	4.731%	$36.4883	$36.49	$36.50	$36.50
Purchase #4	$236.76	12.384%	$266.0804	$266.08	$266.10	$266.10
Purchase #5	$63.55	13.169%	$71.9189	$71.92	$71.90	$71.90
Purchase #6	$246.54	7.770%	$265.6962	$265.70	$265.70	$265.70
Purchase #7	$88.50	13.137%	$100.1262	$100.13	$100.15	$100.10
7 purchase totals =	$760.00		$836.4726	$836.49	$836.50	$836.50