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	$139.99	7.297%	$150.2051	$150.21	$150.20	$150.20
Purchase #2	$165.36	12.334%	$185.7555	$185.76	$185.75	$185.80
Purchase #3	$75.80	3.603%	$78.5311	$78.53	$78.55	$78.50
Purchase #4	$61.95	8.763%	$67.3787	$67.38	$67.40	$67.40
Purchase #5	$153.44	13.133%	$173.5913	$173.59	$173.60	$173.60
Purchase #6	$233.77	7.814%	$252.0368	$252.04	$252.05	$252.00
Purchase #7	$57.84	3.244%	$59.7163	$59.72	$59.70	$59.70
7 purchase totals =	$888.15		$967.2148	$967.23	$967.25	$967.20