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	$84.49	4.863%	$88.5987	$88.60	$88.60	$88.60
Purchase #2	$122.90	6.287%	$130.6267	$130.63	$130.65	$130.60
Purchase #3	$221.80	3.280%	$229.075	$229.08	$229.10	$229.10
Purchase #4	$111.40	10.436%	$123.0257	$123.03	$123.05	$123.00
Purchase #5	$75.61	8.794%	$82.2591	$82.26	$82.25	$82.30
Purchase #6	$120.94	11.166%	$134.4442	$134.44	$134.45	$134.40
Purchase #7	$62.96	13.649%	$71.5534	$71.55	$71.55	$71.60
7 purchase totals =	$800.10		$859.5828	$859.59	$859.65	$859.60