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	$12.43	4.674%	$13.011	$13.01	$13.00	$13.00
Purchase #2	$143.87	5.337%	$151.5483	$151.55	$151.55	$151.50
Purchase #3	$131.53	12.589%	$148.0883	$148.09	$148.10	$148.10
Purchase #4	$78.48	13.721%	$89.2482	$89.25	$89.25	$89.20
Purchase #5	$31.49	7.678%	$33.9078	$33.91	$33.90	$33.90
Purchase #6	$198.34	6.658%	$211.5455	$211.55	$211.55	$211.50
Purchase #7	$167.76	3.159%	$173.0595	$173.06	$173.05	$173.10
7 purchase totals =	$763.90		$820.4086	$820.42	$820.40	$820.30