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	$55.71	6.739%	$59.4643	$59.46	$59.45	$59.50
Purchase #2	$113.33	5.462%	$119.5201	$119.52	$119.50	$119.50
Purchase #3	$101.89	4.184%	$106.1531	$106.15	$106.15	$106.20
Purchase #4	$20.98	10.802%	$23.2463	$23.25	$23.25	$23.20
Purchase #5	$65.80	7.158%	$70.51	$70.51	$70.50	$70.50
Purchase #6	$54.97	7.442%	$59.0609	$59.06	$59.05	$59.10
Purchase #7	$123.68	6.304%	$131.4768	$131.48	$131.50	$131.50
7 purchase totals =	$536.36		$569.4315	$569.43	$569.40	$569.50