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	$5.32	10.317%	$5.8689	$5.87	$5.85	$5.90
Purchase #2	$91.49	9.839%	$100.4917	$100.49	$100.50	$100.50
Purchase #3	$128.45	10.377%	$141.7793	$141.78	$141.80	$141.80
Purchase #4	$55.43	6.437%	$58.998	$59.00	$59.00	$59.00
Purchase #5	$231.39	8.293%	$250.5792	$250.58	$250.60	$250.60
Purchase #6	$74.56	3.366%	$77.0697	$77.07	$77.05	$77.10
Purchase #7	$157.88	3.529%	$163.4516	$163.45	$163.45	$163.50
7 purchase totals =	$744.52		$798.2384	$798.24	$798.25	$798.40