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	$143.92	13.507%	$163.3593	$163.36	$163.35	$163.40
Purchase #2	$106.52	4.632%	$111.454	$111.45	$111.45	$111.50
Purchase #3	$69.83	4.400%	$72.9025	$72.90	$72.90	$72.90
Purchase #4	$96.71	4.239%	$100.8095	$100.81	$100.80	$100.80
Purchase #5	$233.49	13.626%	$265.3053	$265.31	$265.30	$265.30
Purchase #6	$48.92	4.350%	$51.048	$51.05	$51.05	$51.00
Purchase #7	$23.88	8.552%	$25.9222	$25.92	$25.90	$25.90
7 purchase totals =	$723.27		$790.8008	$790.80	$790.75	$790.80