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	$131.45	9.599%	$144.0679	$144.07	$144.05	$144.10
Purchase #2	$226.52	7.165%	$242.7502	$242.75	$242.75	$242.80
Purchase #3	$130.37	9.316%	$142.5153	$142.52	$142.50	$142.50
Purchase #4	$153.98	6.631%	$164.1904	$164.19	$164.20	$164.20
Purchase #5	$216.80	5.697%	$229.1511	$229.15	$229.15	$229.20
Purchase #6	$149.76	12.688%	$168.7615	$168.76	$168.75	$168.80
Purchase #7	$69.43	13.491%	$78.7968	$78.80	$78.80	$78.80
7 purchase totals =	$1,078.31		$1,170.2332	$1,170.24	$1,170.20	$1,170.40