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	$74.75	5.178%	$78.6206	$78.62	$78.60	$78.60
Purchase #2	$247.71	13.588%	$281.3688	$281.37	$281.35	$281.40
Purchase #3	$125.51	6.789%	$134.0309	$134.03	$134.05	$134.00
Purchase #4	$55.32	4.650%	$57.8924	$57.89	$57.90	$57.90
Purchase #5	$100.46	12.530%	$113.0476	$113.05	$113.05	$113.00
Purchase #6	$135.30	4.457%	$141.3303	$141.33	$141.35	$141.30
Purchase #7	$103.53	9.278%	$113.1355	$113.14	$113.15	$113.10
7 purchase totals =	$842.58		$919.4261	$919.43	$919.45	$919.30